Nodule organogenesis is a complex developmental process which is induced post-embryonically following rhizobia infection and relies on coordinated action of a suite of transcription factors at multiple stages starting from its initiation, de novo meristem establishment and differentiation. The rewiring of nitrate-responsive NIN-LIKE PROTEIN (NLP) homolog, NODULE INCEPTION (NIN) transcription factor through genetic adaptations in the common ancestor of the nitrogen-fixing clade is crucial to the origin of nodulation trait. Moreover, nodule formation emerged through the co-option of evolutionary ancient root/lateral root developmental pathways mediated by conserved transcriptional regulators such as NF-Y, LBD16, SHR/SCR, WOX5, PLT and KNOX. Importantly, NIN has acquired functions to integrate signals from rhizobia infection and divert the existing developmental pathways towards nodule organogenesis, thereby acts as a master regulator of root nodule symbiosis. Nodule specific innovations in the existing developmental pathway genes through mechanisms like genetic adaptations in their cis-regulatory region, paralog retention, changes in spatio-temporal gene expression pattern and functional changes to the protein are crucial for imparting developmental novelty during nodule organogenesis. Here, we provide a consolidated idea on transcription factor–mediated genetic modules regulating distinct stages of nodule organogenesis with an emphasis on their nodule specific innovations. This knowledge gain is particularly important to engineer nitrogen-fixing nodules into non-nodulation crop plants which will eventually minimize the reliance on synthetic nitrogen fertilizers and thereby favors a sustainable agricultural system. Nodule organogenesis evolved through co-option of existing developmental pathway genes with specific genetic adaptations ensuring its developmental novelty.

Symbiosis receptor kinase (SYMRK), a malectin-like-domain/leucine-rich-repeat receptor-like-kinase (MLD-LRR-RLK), is the upstream-most component in the common-symbiosis-signaling-pathway. We highlight 2 proline residues that were distinctly acquired by SYMRK orthologs in its hinge regions to constitute a signaling module for allowing progress of symbionts across transcellular barriers during rhizobia-legume symbiosis. Within the ectodomain hinge (EctoD-hinge), all MLD-LRR-RLKs have a conserved W1xnGDPCxnW2×4C motif, where SYMRK orthologs within legumes have a distinct signature with a proline preceding W2 enabling cleavage of SYMRK ectodomain for releasing MLD. Within the kinase hinge (KD-hinge) at gatekeeper + 1 position, a conserved glutamate in MLD-LRR-RLKs is replaced by proline in all SYMRK orthologs that enabled its dual-specific kinase activity for ensuring ectodomain cleavage. Substitution of either proline restricted cortical progression of symbionts, forming infection patches in the nodule apex without affecting epidermal invasion and nodule organogenesis. This halt was entirely overcome by ectopic expression of free MLD, demonstrating the released MLD has an active role in progress of symbionts. Overall, we show that conservation of distinct prolines in hinge regions of SYMRK orthologs in legumes generates a signaling module involving dimerization and optimal phosphorylation of SYMRK for releasing MLD as an active transducer of symbiosis signaling.

Root branching and lateral root formation aided successful colonization of land plants in terrestrial ecosystems, eventually resulting in the origin of an adaptive trait called nodulation in specific land plant lineages. Nodule and lateral root formations involve de novo organogenesis, which is induced post-embryonically with coordinated steps of cell division and differentiation. There are substantial resemblances between the initiation of nodule and lateral root, including the types of root cell lineages that acquire mitotic competence to induce new organ formation and the pattern of formative division within the incipient organ primordia, both converging on a localized auxin response. The recruitment of specific genetic modules of lateral root developmental pathways during nodule organogenesis corroborates their evolutionary origin as modified lateral roots. However, such genetic modules are likely to be regulated differentially depending on the acquisition of nodulation-specific adaptations to ensure novelty in nodule organogenesis. Despite commonalities, these two lateral organs have differential morphology, vascular organizations, and functions due to the acquisition of different organ identities, suggesting involvement of distinct differentiation pathways during the maturation of both these organs. The current review provides a consolidated idea of the recent advances in nodule development with its resemblance to lateral root formation, emphasizing the shared and unique genetic regulators involved from their inception to maturation.

Symbiosis Receptor Kinase (SYMRK), a malectin-like-domain/leucine-rich-repeat receptor-like-kinase (MLD-LRR-RLK), is the upstream most component in Common-Symbiosis-Signalling-Pathway. We highlight two Proline residues that were distinctly acquired by SYMRK orthologues in its hinge-regions to evolve a signalling module for allowing progress of symbionts across transcellular barriers during rhizobia-legume symbiosis. Within the Ectodomain hinge (EctoD-hinge) all MLD-LRR-RLKs have a conserved W1xnGDPCxnW2x4C motif, where SYMRK orthologues within legumes have a distinct signature with a Proline preceding W2 enabling cleavage of SYMRK-EctoD for releasing MLD. Within the kinase hinge (KD-hinge) at gatekeeper+1 position, a conserved Glutamate in MLD-LRR-RLKs is replaced by Proline in all SYMRK orthologues that enabled its dual-specific kinase activity for ensuring EctoD-cleavage. Substitution of either Proline restricted symbionts at the transcellular epidermal-cortical barrier forming infection patches in the nodule apex without affecting epidermal invasion and nodule organogenesis. This halt was entirely overcome by ectopic expression of free MLD demonstrating the released MLD to have an active role in progress of symbionts. Overall, we show that adaptations of distinct Prolines in hinge-regions of SYMRK orthologues in legumes have evolved a signalling module involving dimerization and optimal phosphorylation of SYMRK for releasing MLD as an active transducer of symbiosis signalling.

Both sucrose and its nonmetabolizable analog turanose restore root nodule symbiosis in a Medicago truncatula cytokinin perception mutant through induction of an auxin conjugate hydrolase. Rhizobia-legume interactions recruit cytokinin for the induction of nodule primordia in the cortex. Cytokinin signaling regulates auxin transport and biosynthesis, causing local auxin accumulation, which triggers cortical cell division. Since sugar signaling can trigger auxin responses, we explored whether sugar treatments could rescue symbiosis in the Medicago truncatula cytokinin response 1 (cre1) mutant. Herein, we demonstrate that sucrose and its nonmetabolizable isomer turanose can trigger auxin response and recover functional symbiosis in cre1, indicating sucrose signaling to be necessary for the restoration of symbiosis. In both M. truncatula A17 (wild type) and cre1, sucrose signaling significantly upregulated IAA-Ala Resistant 3 (IAR33), encoding an auxin conjugate hydrolase, in rhizobia-infected as well as in uninfected roots. Knockdown of IAR33 (IAR33-KD) significantly reduced nodulation in A17, highlighting the importance of deconjugation-mediated auxin accumulation during nodule inception. In cre1, IAR33-KD restricted the sucrose-mediated restoration of functional symbiosis, suggesting that deconjugation-mediated auxin accumulation plays a key role in the absence of CRE1-mediated auxin biosynthesis and transport control. Overexpression of IAR33 also restored functional symbiosis in cre1, further suggesting that IAR33 mediates auxin accumulation in response to sucrose signaling. Since all the observed sucrose-mediated responses were common to A17 and cre1, deconjugation-mediated auxin response appeared to be independent of CRE1, which normally governs local auxin accumulation in the presence of rhizobia. We propose that sucrose-dependent restoration of symbiosis in cre1 occurs by the activation of IAR33-mediated auxin deconjugation.

EDITORIAL article Front. Plant Sci., 29 May 2023Sec. Plant Symbiotic Interactions Volume 14 - 2023 | https://doi.org/10.3389/fpls.2023.1208904

Nitrogenase that catalyses anaerobic symbiotic nitrogen fixation (SNF) in legumes is synthesized by rhizobium. Legume root cells express nodulin proteins after infection with rhizobia. Nodulins have been classified as early and late, reflecting the time points of their expression. Leghemoglobin (LegH), which is a classic example of a late nodulin, sequesters oxygen inside the nodule to protect the nitrogenase from oxygen toxicity to sustain SNF. Previous data from our laboratory demonstrated that phosphorylated LegH at S45 showed compromised oxygen sequestration in vitro due to structural disruption of the porphyrin binding pocket responsible for its oxygen binding. Moreover, we have demonstrated by using co-immunoprecipitation that LegH interacts both in vitro with Nodulin 16 of Lotus japonicus (Nlj16), another late nodulin. Fluorescence Immunohistochemistry (IHC) data shows that both LegH and Nlj16 are localized in the membrane and cytosol of infected cells. Notably, serine phosphorylation of LegH and interaction of Nlj16 with LegH respectively reduces and increases its in vitro oxygen sequestration ability. In this report, to further elucidate the spatio-temporal regulation of this interaction, we generated hairy root transgenic Lotus japonicus plants where Nlj16 has been knocked down by using siRNA. Most interestingly, our data shows that the membrane localization of LegH is obliterated in the Nlj16 knocked-down root cells infected with the cognate Rhizobia suggesting a distinct role of Nlj16 in its recruitment to the membrane of nodule cells.

Dalbergoids are typified by crack-entry symbiosis which is evidenced to be Nod Factor (NF)-independent in several Aeschynomene legumes. Natural symbionts of the dalbergoid legume Arachis hypogaea are always NF-producing, prompting us to check whether symbiosis in this legume could also be NF-independent. For this, we followed the symbiosis with two NF-containing bradyrhizobial strains - SEMIA6144, a natural symbiont of Arachis and ORS285, a versatile nodulator of Aeschynomene legumes, along with their corresponding nodulation (nod) mutants. Additionally, we investigated NF-deficient bradyrhizobia like BTAi1, a natural symbiont of Aeschynomene indica and the WBOS strains that were natural endophytes of Oryza sativa, collected from an Arachis-Oryza intercropped field. While SEMIA6144ΔnodC was non-nodulating, both ORS285 and ORS285ΔnodB could induce functional nodulation, although with lower efficiency than SEMIA6144. On the other hand, all the NF-deficient strains - BTAi1, WBOS2 and WBOS4 showed comparable nodulation with ORS285 indicating Arachis to harbour an NF-independent mechanism of symbiosis. Intriguingly, symbiosis in Arachis, irrespective of whether it was NF-dependent or independent, was always associated with the curling or branching of the rosette root hairs at the lateral root bases. Thus, despite being predominantly described as an NF-dependent legume, Arachis does retain a vestigial, less-efficient form of NF-independent symbiosis.

Jasmonate ZIM domain (JAZ) proteins are the key negative regulators of jasmonate signaling, an important integrator of plant–microbe relationships. Versatility of jasmonate signaling outcomes are maintained through the multiplicity of JAZ proteins and their definitive functionalities. How jasmonate signaling influences the legume-Rhizobium symbiotic relationship is still unclear. In Arachis hypogaea (peanut), a legume plant, one JAZ sub-family (JAZ1) gene and one TIFY sequence containing protein family member (TIFY8) gene show enhanced expression in the early stage and late stage of root nodule symbiosis (RNS) respectively. In plants, JAZ sub-family proteins belong to a larger TIFY family. Here, this study denotes the first attempt to reveal in planta interactions of downstream jasmonate signaling regulators through proteomics and mass spectrometry to find out the mode of jasmonate signaling participation in the RNS process of A. hypogaea. From 4-day old Bradyrhizobium-infected peanut roots, the JAZ1-protein complex shows its contribution towards the rhizobial entry, nodule development, autoregulation of nodulation and photo-morphogenesis during the early stage of symbiosis. From 30-day old Bradyrhizobium infected roots, the TIFY8-protein complex reveals repressor functionality of TIFY8, suppression of root jasmonate signaling, modulation of root circadian rhythm and nodule development. Cellular localization and expression level of the interaction partners during the nodulation process further substantiate the in planta interaction pairs. This study provides a comprehensive insight into the jasmonate functionality in RNS through modulation of nodule number and development, during the early stage and root circadian rhythm during the late stage of nodulation, through the protein complexes of JAZ1 and TIFY8 respectively in A. hypogaea.

The long noncoding RNA ENOD40 is required for cortical cell division during root nodule symbiosis (RNS) of legumes, though it is not essential for actinorhizal RNS. Our objective was to understand whether ENOD40 was required for aeschynomenoid nodule formation in Arachis hypogaea. AhENOD40 express from chromosome 5 (chr5) (AhENOD40-1) and chr15 (AhENOD40-2) during symbiosis, and RNA interference of these transcripts drastically affected nodulation, indicating the importance of ENOD40 in A. hypogaea. Furthermore, we demonstrated several distinct characteristics of ENOD40. (i) Natural antisense transcript (NAT) of ENOD40 was detected from the AhENOD40-1 locus (designated as NAT-AhDONE40). (ii) Both AhENOD40-1 and AhENOD40-2 had two exons, whereas NAT-AhDONE40 was monoexonic. Reverse-transcription quantitative PCR analysis indicated both sense and antisense transcripts to be present in both cytoplasm and nucleus, and their expression increased with the progress of symbiosis. (iii) RNA pull-down from whole cell extracts of infected roots at 4 days postinfection indicated NAT-AhDONE40 to interact with the SET (Su(var)3-9, enhancer of Zeste and Trithorax) domain containing absent small homeotic disc (ASH) family protein AhASHR3 and this interaction was further validated using RNA immunoprecipitation and electrophoretic mobility shift assay. (iv) Chromatin immunoprecipitation assays indicate deposition of ASHR3-specific histone marks H3K36me3 and H3K4me3 in both of the ENOD40 loci during the progress of symbiosis. ASHR3 is known for its role in optimizing cell proliferation and reprogramming. Because both ASHR3 and ENOD40 from legumes cluster away from those in actinorhizal plants and other nonlegumes in phylogenetic distance trees, we hypothesize that the interaction of DONE40 with ASHR3 could have evolved for adapting the nodule organogenesis program for legumes. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Nitrogen is one of the essential plant nutrients and a major factor limiting crop productivity. To meet the requirements of sustainable agriculture, there is a need to maximize biological nitrogen fixation in different crop species. Legumes are able to establish root nodule symbiosis (RNS) with nitrogen-fixing soil bacteria which are collectively called rhizobia. This mutualistic association is highly specific, and each rhizobia species/strain interacts with only a specific group of legumes, and vice versa. Nodulation involves multiple phases of interactions ranging from initial bacterial attachment and infection establishment to late nodule development, characterized by a complex molecular signalling between plants and rhizobia. Characteristically, legumes like groundnut display a bacterial invasion strategy popularly known as "crack-entry'' mechanism, which is reported approximately in 25% of all legumes. This article accommodates critical discussions on the bacterial infection mode, dynamics of nodulation, components of symbiotic signalling pathway, and also the effects of abiotic stresses and phytohormone homeostasis related to the root nodule symbiosis of groundnut and Bradyrhizobium. These parameters can help to understand how groundnut RNS is programmed to recognize and establish symbiotic relationships with rhizobia, adjusting gene expression in response to various regulations. This review further attempts to emphasize the current understanding of advancements regarding RNS research in the groundnut and speculates on prospective improvement possibilities in addition to ways for expanding it to other crops towards achieving sustainable agriculture and overcoming environmental challenges.

In root-nodule symbiosis, rhizobial invasion and nodule organogenesis is host controlled. In most legumes, rhizobia enter through infection threads and nodule primordium in the cortex is induced from a distance. But in dalbergoid legumes like Arachis hypogaea, rhizobia directly invade cortical cells through epidermal cracks to generate the primordia. Herein, we report the transcriptional dynamics with the progress of symbiosis in A. hypogaea at 1 day postinfection (dpi) (invasion), 4 dpi (nodule primordia), 8 dpi (spread of infection in nodule-like structure), 12 dpi (immature nodules containing rod-shaped rhizobia), and 21 dpi (mature nodules with spherical symbiosomes). Expression of putative ortholog of symbiotic genes in 'crack entry' legume A. hypogaea was compared with infection thread-adapted model legumes. The contrasting features were i) higher expression of receptors like LYR3 and EPR3 as compared with canonical Nod factor receptors, ii) late induction of transcription factors like NIN and NSP2 and constitutive high expression of ERF1, EIN2, bHLH476, and iii) induction of divergent pathogenesis-responsive PR-1 genes. Additionally, symbiotic orthologs of SymCRK, ROP6, RR9, SEN1, and DNF2 were not detectable and microsynteny analysis indicated the absence of a RPG homolog in diploid parental genomes of A. hypogaea. The implications are discussed and a molecular framework that guides crack-entry symbiosis in A. hypogaea is proposed.

Plant receptor-like kinases (RLKs) have a Tyr in the "gatekeeper" position adjacent to the hinge region. The gatekeeper is phosphorylated in several RLKs, including symbiosis receptor kinase (SYMRK), but the significance of this remains unknown. Gatekeeper substitution did not inactivate Arachis hypogaea SYMRK but affected autophosphorylation at selected sites. Herein, we show that nonphosphorylatable gatekeepers (Y670F and Y670A) restrict SYMRK to be a Ser/Thr kinase with a basal level of phosphorylation (∼5 P/polypeptide, termed state I) whereas phosphorylatable gatekeepers (Y670 and Y670T) allowed SYMRK to be dual specific (Ser/Thr/Tyr) with a maximal level of phosphorylation (∼10 P/polypeptide, termed state II). State II SYMRKs were phosphorylated on gatekeeper residues, and the phosphocode in their activation segment was distinct from state I. The kcat/ Km for substrate phosphorylation was ∼10-fold higher for state II, though for autophosphorylation, it was comparable with those of state I SYMRKs. To identify other determinants of state I features, we mutagenized all nine sites where phosphorylation was affected by nonphosphorylatable gatekeepers (Y670F and Y670A). Only two such mutants, S754A and S757A, located on the activation loop failed to phosphorylate gatekeeper Tyr and restricted SYMRK in state I. Double mutants like Y670F/S754A retained the features of state I, but Y670F/S757A was significantly inactivated, indicating a nonphosphorylatable gatekeeper can bypass phosphorylation of S754 but not S757 in the activation segment. We propose a working model for the hierarchical phosphorylation of SYMRK on gatekeeper and activation segments for its pS757-mediated activation as a Ser/Thr kinase in selfie mode (autophosphorylation) to a pS754/pY670-mediated activation as a Ser/Thr/Tyr kinase that functions in dual mode (both autophosphorylation and substrate phosphorylation).

Root nodule symbiosis in legumes is established following interaction of compatible rhizobia that activates an array of genes, commonly known as symbiotic-pathway, resulting in nodule development. In model legumes, bacterial entry mainly occurs through infection thread involving the expression of transcription factor CYCLOPS/IPD3. Here we show the functional analysis of AhCYCLOPS in Arachis hypogaea where bacteria invade roots through epidermal cracks. Exploiting significant cross-species domain conservation, trans-complementation experiments involving ectopic expression of AhCYCLOPS in transgenic hairy-roots of Medicago truncatula ipd3 mutants resulted in functional complementation of Medicago nodules. Moreover, native promoter of AhCYCLOPS was sufficient for this cross-species complementation irrespective of the different modes of infection of roots by rhizobia and nodule ontology. To unravel the role of AhCYCLOPS during 'crack-entry' nodulation in A. hypogaea, RNAi of AhCYCLOPS was performed which resulted in delayed nodule inception followed by drastic reduction in nodule number on transgenic hairy-roots. The infection zone of a significant number of RNAi nodules showed presence of infected cells with enlarged nucleus and rod shaped undifferentiated bacteria. Expression analysis showed downregulation of several nodulation responsible effectors endorsing the compromised condition of RNAi roots. Together, the results indicated that AhCYCLOPS plays an important role in A. hypogaea nodule development.

Rhizobia-legume interaction recruits cytokinin for the induction of nodule primordia in the cortex. In , cytokinin signalling involves flavonoid mediated local alteration of polar auxin transport for triggering cortical cell division. Since sugar signalling is widely evidenced to trigger auxin responses, we explored whether sugar treatment could compensate for cytokinin signalling in cytokinin perception mutant Herein we demonstrate that turanose, a non-metabolizable sucrose analogue can trigger auxin response and show signs of recovery of symbiosis in Additionally, turanose upregulated the expression of WUSCHEL-related homeobox 5 () which prompted us to check if overexpression of WOX5 could rescue . Intriguingly, while overexpression of failed, WOX5 from () completely restored functional symbiosis in with an efficiency resembling the wildtype. This indicate that indeterminate and determinate WOX5 responds to differential cues for nodule development and is consistent with their distinct clustering in distance trees. The mechanism of compensation of cytokinin signalling for recovery of symbiosis in was distinct for turanose treatment and expression. Turanose increased level by ∼5-fold and doubled the level of whereas elevated the level of by ∼12-fold without affecting the level of . Thus, turanose compensated MtCRE1 at receptor level whereas WOX5 restored the signalling at the level of response regulators. We propose a working model to discuss how sugar mediated WOX5 signalling have compensated MtCRE1 to recover normal progress of symbiosis

Nod factors (NF) were assumed to be indispensable for the establishment of a rhizobium-legume symbiosis until the discovery that certain Bradyrhizobium strains interacting with certain Aeschynomene species lack the canonical nodABC genes required for their synthesis. So far, the molecular dialogue between Aeschynomene and its symbionts remains an open question. Here we report a time course transcriptional analysis of Aeschynomene evenia in response to inoculation with Bradyrhizobium ORS278. The NF-independent symbiotic process was monitored at five time points between bacterial infection and nodule maturity. The five time points correspond to three specific events, root infection by crack entry, nodule organogenesis, and the establishment of the nitrogen fixing process. During the third stage, about 80 NCR-like genes and eight symbiotic genes known to be involved in signaling, bacterial infection or nodulation regulation were highly expressed. Comparative gene expression analyses at the five time points also enabled the selection of genes with an expression profile that makes them promising markers to monitor early plant responses to bacteria. Such markers could be used in bioassays to identify the nature of the bacterial signal(s). Our data represent valuable resources for investigation of this Nod factor-independent symbiosis.

BACKGROUND:Among semi-aquatic species of the legume genus Aeschynomene, some have the property of being nodulated by photosynthetic Bradyrhizobium lacking the nodABC genes necessary for the synthesis of Nod factors. Knowledge of the specificities underlying this Nod-independent symbiosis has been gained from the model legume Aeschynomene evenia but our understanding remains limited due to the lack of comparative genetics with related taxa using a Nod factor-dependent process. To fill this gap, we combined different approaches to perform a thorough comparative analysis in the genus Aeschynomene.RESULTS:This study significantly broadened previous taxon sampling, including in allied genera, in order to construct a comprehensive phylogeny. In the phylogenetic tree, five main lineages were delineated, including a novel lineage, the Nod-independent clade and another one containing a polytomy that comprised several Aeschynomene groups and all the allied genera. This phylogeny was matched with data on chromosome number, genome size and low-copy nuclear gene sequences to reveal the diploid species and a polytomy containing mostly polyploid taxa. For these taxa, a single allopolyploid origin was inferred and the putative parental lineages were identified. Finally, nodulation tests with different Bradyrhizobium strains revealed new nodulation behaviours and the diploid species outside of the Nod-independent clade were compared for their experimental tractability and genetic diversity.CONCLUSIONS:The extended knowledge of the genetics and biology of the different lineages sheds new light of the evolutionary history of the genus Aeschynomene and they provide a solid framework to exploit efficiently the diversity encountered in Aeschynomene legumes. Notably, our backbone tree contains all the species that are diploid and it clarifies the genetic relationships between the Nod-independent clade and the Nod-dependent lineages. This study enabled the identification of A. americana and A. patula as the most suitable species to undertake a comparative genetic study of the Nod-independent and Nod-dependent symbioses.

Rhizobia-legume interaction activates the SYM pathway that recruits cytokinin signaling for induction of nodule primordia in the cortex. In Arachis hypogaea, bradyrhizobia invade through natural cracks developed in the lateral root base and are directly endocytosed in the cortical cells to generate the nodule primordia. To unravel the role of cytokinin signaling in A. hypogaea, RNA-interference (RNAi) of cytokinin receptor histidine-kinase1 (AhHK1) was done. AhHK1-RNAi downregulated the expression of type-A response regulators such as AhRR5 and AhRR3 along with several symbiotic genes, indicating that both cytokinin signaling and the SYM pathway were affected. Accordingly, there was a drastic downregulation of nodulation in AhHK1-RNAi roots and the nodules that developed were ineffective. These nodules were densely packed, with infected cells having a higher nucleo-cytoplasmic ratio and distinctively high mitotic index, where the rod-shaped rhizobia failed to differentiate into bacteroids within spherical symbiosomes. In accordance with the proliferating state, expression of a mitotic-cyclin AhCycB2.1 was higher in AhHK1-RNAi nodules, whereas expression of a retinoblastoma-related (AhRBR) nodule that restrains proliferation was lower. Also, higher expression of the meristem maintenance factor WUSCHEL-RELATED HOMEOBOX5 correlated with the undifferentiated state of AhHK1-RNAi nodules. Our results suggest that AhHK1-mediated cytokinin signaling is important for both inception and differentiation during nodule development in A. hypogaea.

Cancer‐associated p53 missense mutants confer gain of function (GOF) and promote tumorigenesis by regulating crucial signaling pathways. However, the role of GOF mutant p53 in regulating DNA replication, a commonly altered pathway in cancer, is less explored. Here, we show that enhanced Cdc7‐dependent replication initiation enables mutant p53 to confer oncogenic phenotypes. We demonstrate that mutant p53 cooperates with the oncogenic transcription factor Myb in vivo and transactivates Cdc7 in cancer cells. Moreover, mutant p53 cells exhibit enhanced levels of Dbf4, promoting the activity of Cdc7/Dbf4 complex. Chromatin enrichment of replication initiation factors and subsequent increase in origin firing confirm increased Cdc7‐dependent replication initiation in mutant p53 cells. Further, knockdown of CDC7 significantly abrogates mutant p53‐driven cancer phenotypes in vitro and in vivo. Importantly, high CDC7 expression significantly correlates with p53 mutational status and predicts poor clinical outcome in lung adenocarcinoma patients. Collectively, this study highlights a novel functional interaction between mutant p53 and the DNA replication pathway in cancer cells. We propose that increased Cdc7‐dependent replication initiation is a hallmark of p53 gain‐of‐function mutations. Cancer‐associated p53 missense mutants confer gain‐of‐function (GOF) and promote tumorigenesis. This study shows that one hallmark of p53 GOF mutants is Myb‐dependent transactivation of Cdc7, which leads to enhanced Cdc7/Dbf4‐dependent replication initiation in cancer cells. Cancer‐associated p53 missense mutants confer gain‐of‐function (GOF) and promote tumorigenesis. This study shows that one hallmark of p53 GOF mutants is Myb‐dependent transactivation of Cdc7, which leads to enhanced Cdc7/Dbf4‐dependent replication initiation in cancer cells.

The uphill energy transfer in photosystems implies input energy at higher wavelength leading to energy output at lower wavelength. Briefly, energy is uphill transported from photosystem I (PSI) to photosystem II (PSII), the latter having a lower wavelength emission. This uphill energy transport involves absorption of thermal energy from the surroundings. While such cooling effects have been reported in laser systems we report for the first time a white light driven cooling in thylakoid suspension. The cooling of the surrounding medium by appropriate illumination was illustrated using thermal measurements. Again cooling is inhibited by agents like 3-(3,4-Dichlorophenyl)-1,1-dimethylurea,that block the linear electron flow between the photocenters, implying a dependence of the cooling on interplay between such centers. Furthermore, it is possible to modulate the cooling pattern by addition of external agents like nanopaticles, some favoring further cooling (e.g., Ag nanoparticle) and some like Au or chlorophyll nanoparticles, showing insignificant or even reverse trends. Interestingly, the cooling is invariably associated with the 77K spectra of the thylakoid suspension. With reference to the dark control, an agent causing cooling always increases PSII to PSI ratio and vice versa i.e.,the uphill energy transport. Importantly, the cooling effect, apart from its import role in plant physiology can be exploited artificially for energy saving in post-harvest or food preservation.