Oriented cell divisions are crucial for determining the overall morphology and size of plants, but what controls the onset and duration of this process remains largely unknown. Here, we identified a small molecule that activates root apical meristem (RAM) expression of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE13 (SPL13) a known player in the shoot’s juvenile-to-adult transition. This expression leads to oriented cell divisions in the RAM through SHORT ROOT (SHR) and cell cycle regulators. We further show that the RAM has distinct juvenile and adult phases typed by morphological and molecular characteristics and that SPL factors are crucially required for this transition in Arabidopsis and rice ( Oryza sativa ). In summary, we provide molecular insights into the age-dependent morphological changes occurring in the RAM during phase change.

Transcriptional networks are crucial to integrate various internal and external signals into optimal responses during plant growth and development. In Arabidopsis thaliana, primary root vasculature patterning and proliferation are controlled by a network centred around the basic Helix-Loop-Helix transcription factor complex, formed by TARGET OF MONOPTEROS 5 (TMO5) and LONESOME HIGHWAY (LHW), which control cell proliferation and division orientation by modulating the cytokinin response and other downstream factors. Despite recent progress, many aspects of the TMO5/LHW pathway are not fully understood. In particular, the upstream regulators of TMO5/LHW activity remain unknown. Here, using a forward genetics approach to identify new factors of the TMO5/LHW pathway, we discovered a novel function of the MYB-type transcription factor, MYB12. MYB12 physically interacts with TMO5 and dampens the TMO5/LHW-mediated induction of direct target gene expression, as well as the periclinal/radial cell divisions. The expression of MYB12 is activated by the cytokinin response, downstream of TMO5/LHW, resulting in a novel MYB12-mediated negative feedback loop that restricts TMO5/LHW activity, to ensure optimal cell proliferation rates during root vascular development.

Vascular tissues serve a dual function in plants, both providing physical support and controlling the transport of nutrients, water, hormones, and other small signaling molecules. Xylem tissues transport water from root to shoot; phloem tissues transfer photosynthates from shoot to root; while divisions of the (pro)cambium increase the number of xylem and phloem cells. Although vascular development constitutes a continuous process from primary growth in the early embryo and meristem regions to secondary growth in the mature plant organs, it can be artificially separated into distinct processes including cell type specification, proliferation, patterning, and differentiation. In this review, we focus on how hormonal signals orchestrate the molecular regulation of vascular development in the Arabidopsis primary root meristem. Although auxin and cytokinin have taken center stage in this aspect since their discovery, other hormones including brassinosteroids, abscisic acid, and jasmonic acid also take leading roles during vascular development. All these hormonal cues synergistically or antagonistically participate in the development of vascular tissues, forming a complex hormonal control network.

Transcriptional networks are crucial to integrate various internal and external signals into optimal responses during plant growth and development. Primary root vasculature patterning and proliferation are controlled by a network centred around the basic Helix-Loop-Helix transcription factor complex formed by TARGET OF MONOPTEROS 5 (TMO5) and LONESOME HIGHWAY (LHW), which control cell proliferation and orientation by modulating cytokinin response and other downstream factors. Despite recent progress, many aspects of the TMO5/LHW pathway are not fully understood. In particular, the upstream regulators of TMO5/LHW activity remain unknown. Here, using a forward genetic approach to identify new factors of the TMO5/LHW pathway, we discovered a novel function of the MYB-type transcription factor MYB12. MYB12 physically interacts with TMO5 and dampens the TMO5/LHW-mediated induction of direct target gene expression as well as the periclinal/radial cell divisions. The expression of MYB12 is activated by the cytokinin response, downstream of TMO5/LHW, resulting in a novel MYB12-mediated negative feedback loop that restricts TMO5/LHW activity to ensure optimal cell proliferation rates during root vascular development.

During plant development, a precise balance of cytokinin is crucial for correct growth and patterning, but it remains unclear how this is achieved across different cell types and in the context of a growing organ. Here we show that in the root apical meristem, the TMO5/LHW complex increases active cytokinin levels via two cooperatively acting enzymes. By profiling the transcriptomic changes of increased cytokinin at single-cell level, we further show that this effect is counteracted by a tissue-specific increase in CYTOKININ OXIDASE 3 expression via direct activation of the mobile transcription factor SHORTROOT. In summary, we show that within the root meristem, xylem cells act as a local organizer of vascular development by non-autonomously regulating cytokinin levels in neighbouring procambium cells via sequential induction and repression modules.

Optimal plant growth is hampered by deficiency of the essential macronutrient phosphate in most soils. Plant roots can, however, increase their root hair density to efficiently forage the soil for this immobile nutrient. By generating and exploiting a high-resolution single-cell gene expression atlas of Arabidopsis roots, we show an enrichment of TARGET OF MONOPTEROS 5/LONESOME HIGHWAY (TMO5/LHW) target gene responses in root hair cells. The TMO5/LHW heterodimer triggers biosynthesis of mobile cytokinin in vascular cells and increases root hair density during low-phosphate conditions by modifying both the length and cell fate of epidermal cells. Moreover, root hair responses in phosphate-deprived conditions are TMO5- and cytokinin-dependent. Cytokinin signaling links root hair responses in the epidermis to perception of phosphate depletion in vascular cells.

Spontaneously arising channels that transport the phytohormone auxin provide positional cues for self-organizing aspects of plant development such as flexible vasculature regeneration or its patterning during leaf venation. The auxin canalization hypothesis proposes a feedback between auxin signaling and transport as the underlying mechanism, but molecular players await discovery. We identified part of the machinery that routes auxin transport. The auxin-regulated receptor CAMEL (Canalization-related Auxin-regulated Malectin-type RLK) together with CANAR (Canalization-related Receptor-like kinase) interact with and phosphorylate PIN auxin transporters. camel and canar mutants are impaired in PIN1 subcellular trafficking and auxin-mediated PIN polarization, which macroscopically manifests as defects in leaf venation and vasculature regeneration after wounding. The CAMEL-CANAR receptor complex is part of the auxin feedback that coordinates polarization of individual cells during auxin canalization.

SummaryCortical microtubule (MT) arrays play a critical role in plant cell shape determination by defining the direction of cell expansion. As plants continuously adapt to ever‐changing environmental conditions, multiple environmental and developmental inputs need to be translated into changes of the MT cytoskeleton. Here, we identify and functionally characterize an auxin‐inducible and MT‐localized protein OsIQ67‐DOMAIN14 (OsIQD14), which is highly expressed in rice seed hull cells. We show that while deficiency of OsIQD14 results in short and wide seeds and increases overall yield, overexpression leads to narrow and long seeds, caused by changed MT alignment. We further show that OsIQD14‐mediated MT reordering is regulated by specifically affecting MT dynamics, and ectopic expression of OsIQD14 in Arabidopsis could change the cell shape both in pavement cells and in hypocotyl cells. Additionally, OsIQD14 activity is tightly controlled by calmodulin proteins, providing an alternative way to modify the OsIQD14 activity. Our results indicate that OsIQD14 acts as a key factor in regulating MT rearrangements in rice hull cells and hence the grain shape, and allows effective local cell shape manipulation to improve the rice yield trait.

Geometry and growth and division direction of individual cells are major contributors to plant organ shape and these processes are dependent on dynamics of microtubules (MT). Different MT structures, like the cortical microtubules, preprophase band and mitotic spindle, are characterized by diverse architectural dynamics (Hashimoto, 2015). While several MT binding proteins have been identified that have various effects on MT stability and architecture, they do not discriminate between the different MT structures. It is therefore likely that specific MT binding proteins exist that differentiate between MT structures in order to allow for the differences in architectural dynamics. Although evidence for the effect of specific cues, such as light and auxin, on MT dynamics has been shown in recent years (Lindeboom et al., 2013; Chen et al., 2014), it remains unknown how such cues are integrated and lead to specific effects. Here we provide evidence for how auxin and calcium signaling can be integrated to modulate MT dynamics, by means of IQD proteins. We show that the Arabidopsis IQD15-18 subclade of this family is regulated by auxin signaling, can bind calmodulins in a calcium-dependent manner and are evolutionarily conserved. Furthermore, AtIQD15-18 directly bind SPIRAL2 protein in vitro and in vivo and modulate its function, likely in a calmodulin-dependent way, thereby providing a missing link between two important regulatory pathways of MT dynamics.

AbstractGeometry and growth and division direction of individual cells are major contributors to plant organ shape and these processes are dependent on dynamics of microtubules (MT). Different MT structures, like the cortical microtubules, preprophase band and mitotic spindle, are characterized by diverse architectural dynamics (Hashimoto, 2015). While several MT binding proteins have been identified that have various effects on MT stability and architecture, they do not discriminate between the different MT structures. It is therefore likely that specific MT binding proteins exist that differentiate between MT structures in order to allow for the differences in architectural dynamics. Although evidence for the effect of specific cues, such as light and auxin, on MT dynamics has been shown in recent years (Lindeboomet al., 2013; Chenet al., 2014), it remains unknown how such cues are integrated and lead to specific effects. Here we provide evidence for how auxin and calcium signaling can be integrated to modulate MT dynamics, by means of IQD proteins. We show that theArabidopsisIQD15-18 subclade of this family is regulated by auxin signaling, can bind calmodulins in a calcium-dependent manner and are evolutionarily conserved. Furthermore, AtIQD15-18 directly bind SPIRAL2 proteinin vitroandin vivoand modulate its function, likely in a calmodulin-dependent way, thereby providing a missing link between two important regulatory pathways of MT dynamics.One sentence summaryIQD proteins integrate auxin and calcium signaling, two major signaling pathways, to control the cytoskeleton dynamics and cell shape ofArabidopsis.

Geometry and growth and division direction of individual cells are major contributors to plant organ shape and these processes are dependent on dynamics of microtubules (MT). Different MT structures, like the cortical microtubules, preprophase band and mitotic spindle, are characterized by diverse architectural dynamics ([Hashimoto, 2015][1]). While several MT binding proteins have been identified that have various effects on MT stability and architecture, they do not discriminate between the different MT structures. It is therefore likely that specific MT binding proteins exist that differentiate between MT structures in order to allow for the differences in architectural dynamics. Although evidence for the effect of specific cues, such as light and auxin, on MT dynamics has been shown in recent years ([Lindeboom et al. , 2013][2]; [Chen et al. , 2014][3]), it remains unknown how such cues are integrated and lead to specific effects. Here we provide evidence for how auxin and calcium signaling can be integrated to modulate MT dynamics, by means of IQD proteins. We show that the Arabidopsis IQD15-18 subclade of this family is regulated by auxin signaling, can bind calmodulins in a calcium-dependent manner and are evolutionarily conserved. Furthermore, AtIQD15-18 directly bind SPIRAL2 protein in vitro and in vivo and modulate its function, likely in a calmodulin-dependent way, thereby providing a missing link between two important regulatory pathways of MT dynamics.One sentence summary IQD proteins integrate auxin and calcium signaling, two major signaling pathways, to control the cytoskeleton dynamics and cell shape of Arabidopsis . [1]: #ref-14 [2]: #ref-22 [3]: #ref-8

Cortical microtubule (MT) arrays play a critical role in plant cell shape determination by defining the direction of cell expansion 1-3 . The control of plant organ shape and architecture is a major target of cereal crop improvement. Given the pleiotropic effects of MT modification, however, it is challenging to exploiting MT array organization for crop improvement. Moreover, as plants continuously adapt cell growth and expansion to ever-changing environmental conditions, multiple environmental (e.g. light 4 ) and developmental (e.g. hormones 5,6 ) inputs need to be translated into changes of the MT cytoskeleton. Here, we identify and functionally characterize an auxin-inducible and MT-localized protein OsIQ67-DOMAIN14 (OsIQD14), which is highly expressed in rice seed hull cells. While deficiency of OsIQD14 results in short and wide seeds and increases overall yield, overexpression leads to narrow and long seeds, caused by changes in the direction of MT arrangement. We further show that OsIQD14-mediated MT reordering is regulated through interacting with SPIRAL2, a MT-binding protein involved in KATANIN1-mediated MT rearrangement 7,8 , and with calmodulin proteins. As such, OsIQD14 acts as an integrator of auxin and calcium inputs into MT rearrangements, and allows effective local cell shape manipulation to improve a key rice yield trait.

Rice (Oryza sativa) is the most important crop and feeds more than half of the world population. The architecture of rice, including height, leaf inclination and tiller number, is important for rice planting and yield. Plant hormone, brassinosteroids (BR), plays crucial roles in modulating plant architecture and seed yield. But BR cannot be applied in agriculture production directly because BR regulated multiple processes and could not be transcriptional regulated in different tissues. The rice BR-deficient and BR-insensitive mutants, such as d11, d2 and d61, are dwarf with erect leaves (the ideal architecture for dense planting, Sumiyo et al., 2005; Yamamuro et al., 2000). But BR deficiency/insensitivity also leads to decreased reproductivity and grain yield. Enhanced BR signalling contributes to better nutrition, higher efficiency of carbohydrate transportation from source to sink and increased grain yield. But the increased plant height and leaf inclination induces lodging and reduces planting density. One of solutions is identifying new regulators which can mediate parts of BR-regulated rice growth. Here, we identified a new GATA factor, OsGATA7, modulates BR-mediated growth regulation in architecture and grain shape. GATA factors are a large family of transcriptional regulators found in fungi, animals and plants. All GATA factors feature zinc finger motif (CX2CX17–20CX2C) and the contiguous basic region as DNA binding domain (Reyes et al., 2004). There are 28 and 29 putative GATA members in rice and Arabidopsis, respectively. In Arabidopsis, several GATA factors have been studied. HAN gene regulates WUS expression and boundary formation between meristem and lateral organs. GNC and GNL affect chloroplast content. Overexpression of ZIM leads to elongated hypocotyl and petiole. NIT2 is involved in nitrate-dependent control of transcription. And AtGATA2 functions in light- and BR-regulated photomorphogenesis. In rice, two GATA factors have been functionally characterized. The Cga1 regulates chloroplast development and plant architecture (Hudson et al., 2013) and NL1 modulates organogenesis during reproductive development (Wang et al., 2009). We identified a rice GATA regulator, OsGATA7 (Os10g0557600), which was a member of rice GATA subfamily I. There are two exons and one intron in OsGATA7 genomic DNA, and OsGATA7 protein has one zinc finger/GATA domain located at the C-terminus. qRT-PCR analysis revealed the constitutive expression of OsGATA7 in various tissues, including young/old leaf blade, young/old leaf sheath, leaf lamina joint, young/old root, stem and panicle, with a relatively higher level in young leaf sheath and panicle (Fig. 1a). Studies using transgenic plant harbouring promoter-GUS vector (pOsGATA7-GUS) demonstrated the expression pattern of OsGATA7 in roots, leaves, lamina joint, internodes, lemma and stamens (Fig. 1a). To investigate the physiological functions of OsGATA7, we constructed transgenic lines using artificial microRNA (AM lines) to knock down the expression of OsGATA7 in japonica rice WYJ7. qRT-PCR analysis showed that OsGATA7 expression was repressed in AM lines. AM lines have decreased height and leaf inclination, as well as reduced primary branch, grain number and grain weights (Fig. 1b, c, and f). Also we constructed genome-edited lines using CRISPR/Cas9 (CRI lines) technology in WYJ7. Sequencing results illustrated two CRI lines (CRI7-1 and CRI7-5) had mutations and generated stop site in the exons. CRI lines have obviously decreased height and leaf inclination (Fig. 1g), illustrating more stunted and compact architecture than wild type (more significantly than AM lines). CRI lines have reduced primary branch, secondary branch (no significant difference in AM lines), grain number and grain weight (Fig. 1h, i and l), similar to AM lines. It seemed that the architecture and grain number/weight of AM and CRI lines are similar to weak alleles of BR-deficient/insensitive mutants. In addition, the root length of AM seedling is much shorter than WT (Fig. 1m). When treated with eBL (epi-brassinolide), root growth is less severely inhibited in the AM seedling than WT (Fig. 1m), suggesting AM lines are less sensitive to BR. qRT-PCR also illustrated BR-regulated expression of OsGATA7 (Fig. 1n). Above all, the architecture, the branch/grain number, the grain weight, the BR sensitivity and BR-regulated gene expression together supposed that OsGATA7 was involved in BR-mediated plant growth regulation. Although OsGATA7 AM and CRI lines have some phenotypes similar to BR-deficient/insensitive mutants and show interfered BR signal and response, these lines have better growth condition than reported BR-related mutants, indicating OsGATA7 has not as severe influences as BR signalling in rice growth, especially in reproductive development. Even the grain number and weight are slightly lower in individual plant of AM and CRI1 lines, and the selfed-seed fertilities of CRI1 lines were slightly lower than WT (AM lines were similar to WT), the yield analysis still illustrated that the grain weight of CRI lines was higher (30.4% and 43.3% in CRI7-1 and CRI-5 line) than wild type in the same area (Fig. 1l) because of dense planting as these lines have compact architecture. Besides, the grains (as well as brown rice) produced from AM lines (Fig. 1d and e) and CRI lines (Fig. 1j and k) are longer and narrower than WT. Detailed analysis of the outer epidermal cell showed that AM lines had increased cell number (Fig. 1q) but not cell elongation, whereas BR was considered to mainly induce cell elongation. Grain shape is a preference which links to rice quality. Our statistical analysis (Fig. 1o and p) further demonstrated that BR-insensitive mutant d61 had shorter and round grain, suggesting that OsGATA7 played different roles in grain shape regulation with BR signalling. Taken together, OsGATA7 functions in controlling rice plant architecture and panicle/grain development and the knock-down/genome-edited lines have ideal traits of both architecture and grain shape. The CRI lines have enhanced grain yield than WT. As well as AM and CRI lines, we also constructed the overexpression lines of OsGATA7 (pUbi-OsGATA7). There was no significant phenotype in adult plant of overexpression lines, which might be because that the increased OsGATA7 transcription level in wild type would not be enough to induce growth phenotypes or OsGATA7 worked with other partners and could not induce growth phenotypes by overexpressing it alone. Many literatures reported Arabidopsis BR-deficient or BR-insensitive mutants have phenotypes of dwarf, round leaves, shorter petioles and reduced reproductively. Overexpression of OsGATA7 could partially rescue phenotypes of Arabidopsis BR-insensitive mutant bri1-5, such as plant height (Fig. 1r), round leaves and short petioles, but not rosette leaf sides (important for Arabidopsis plant density), which further suggested that OsGATA7 enhanced BR signalling and partially modulated BR-mediated plant growth in some processes. Above all, OsGATA7 is a multifunction gene regulating rice growth. The plant height, leaf inclination, panicle development and grain number/shape/weight of OsGATA7 knock-down/genome-edited lines suggest OsGATA7 is involved in BR-mediated growth regulation. Interestingly, BR positively regulates OsGATA7 expression, and OsGATA7 also affects BR signalling and sensitivity, indicating BR and OsGATA7 synergistically regulate some processes of rice growth. But OsGATA7 has diverse functions in others processes, such as grain shape regulation, indicating that OsGATA7 has only partial overlap with BR signalling regulation of rice growth. Partially rescued phenotypes of Arabidopsis bri1-5 mutant by OsGATA7 overexpression further demonstrated that OsGATA7 modulated some BR-mediated growth regulations, and OsGATA7 also had BR-independent regulation in plant growth, especially in reproductive growth. AM and CRI lines are suitable for dense planting because of the ideal architecture, especially CRI lines (more compact than AM lines). The enhanced plant number in the same area, and no severe reduced grain weight and number in individual plant, increases the grain yield in the unit area obviously. And so far we did not observe that the AM and CRI1 lines are more sensitive to pathogen/herbivore or abiotic stress, which mean they would be putative candidate lines for breeding. Taken together, our work identified OsGATA7 functioning in BR-mediated architecture regulation, panicle development and grain shape/number/weight/yield. OsGATA7 modulates BR-mediated rice growth regulation and avoids side-effects of BR signalling, which would be a putative candidate gene for potentially using in agriculture production as OsGATA7 knock-down/genome-edited lines have ideal architecture, better grain shape, and enhanced grain yield. This work was supported by the National Basic Research Program of China (grant no. 2014CB943404), Ministry of Agriculture of China (grant no. 2009ZX08009–022B), National Natural Science Foundation of China (grant no. 31761163003, 31371469 and 31671660), the SMC-Funding of Shanghai Jiao Tong University, and the China Scholarship Council. We thank Shu-Ping Xu (SIPPE) for assisting with rice transformation. The authors declare no conflict of interest.

Receptor-like protein ELT1 promotes brassinosteroid signaling through interacting with and suppressing the endocytosis-mediated degradation of receptor BRI1

The plant hormone auxin is perceived by the nuclear F-box protein TIR1 receptor family and regulates gene expression through degradation of Aux/IAA transcriptional repressors. Several studies have revealed the importance of the proteasome in auxin signalling, but details on how the proteolytic machinery is regulated and how this relates to degradation of Aux/IAA proteins remains unclear. Here we show that an Arabidopsis homologue of the proteasome inhibitor PI31, which we name PROTEASOME REGULATOR1 (PTRE1), is a positive regulator of the 26S proteasome. Loss-of-function ptre1 mutants are insensitive to auxin-mediated suppression of proteasome activity, show diminished auxin-induced degradation of Aux/IAA proteins and display auxin-related phenotypes. We found that auxin alters the subcellular localization of PTRE1, suggesting this may be part of the mechanism by which it reduces proteasome activity. Based on these results, we propose that auxin regulates proteasome activity via PTRE1 to fine-tune the homoeostasis of Aux/IAA repressor proteins thus modifying auxin activity.

Brassinosteroids (BRs) play key roles in plant growth and development, and regulate various agricultural traits. Enhanced BR signaling leads to increased seed number and yield in Arabidopsis bzr1-1D (AtBZR1P234L, gain-of-function mutant of the important transcription factor in BR signaling/effects). BR signal transduction pathway is well elucidated in Arabidopsis but less known in other species. Soybean is an important dicot crop producing edible oil and protein. Phylogenetic analysis reveals AtBZR1-like genes are highly conserved in angiosperm and there are 4 orthologues in soybean (GmBZL1-4). We here report the functional characterization of GmBZL2 (relatively highly expresses in flowers). The P234 site in AtBZR1 is conserved in GmBZL2 (P216) and mutation of GmBZL2P216L leads to GmBZL2 accumulation. GmBZL2P216L (GmBZL2*) in Arabidopsis results in enhanced BR signaling; including increased seed number per silique. GmBZL2* partially rescued the defects of bri1-5, further demonstrating the conserved function of GmBZL2 with AtBZR1. BR treatment promotes the accumulation, nuclear localization and dephosphorylation/phosphorylation ratio of GmBZL2, revealing that GmBZL2 activity is regulated conservatively by BR signaling. Our studies not only indicate the conserved regulatory mechanism of GmBZL2 and BR signaling pathway in soybean, but also suggest the potential application of GmBZL2 in soybean seed yield.

At high excitation intensity the photoluminescence (PL) spectra of ZnCdSe/ZnSe multiple quantum wells were studied, which showed strong excitonic emission and a broad emission band at low energy side. The dependence of the broad emission band on excitation intensity shoed obviously that the broad emission band is related to impurity. In time resolved luminescence spectra, with increasing the delay times (ns), the broad emission band shifts to low energy side and full width at half maximum decreased, which showed the typical characteristic of donor-acceptor pairs (DAP) emission. And then, the reason that the excitonic emission peak and the DAP band decay with same speed was discussed and it was attributed to the free carriers relax effect.

Blue-green and blue stimulated emission under photopumping in Zn0.8Cd0.2Se-ZnSe and ZnSe-ZnS multiple quantum wells (MQWs) on (100) GaAs substrate grown by atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD) have been investigated, respectively. For the Zn0.8Cd0.2Se-ZnSe MQWs, the stimulated emission of the sample with different cavity length is observed at 77K, two groups of stimulated emission lines observed are attributed to n equals 1 heavy- hole (hh) and light-hole (lh) exciton transition, respectively, and it is noticed that the sample with the shorter Fabry-Perot cavity length has the larger threshold excitation and more mode spacing. For the ZnSe-ZnS MQWs, the blue stimulated emission is observed and attributed to the exciton-exciton interactions.