SHOOT MERISTEMLESS (STM), a homeobox transcription factor, functions to maintain shoot apical meristem (SAM) and floral meristem (FM) activity. Carpel formation is abolished in stm mutant flowers, but this phenotype can be partially restored by compromising the function of SERRATE (SE), the core component in miRNA formation. However, whether and how SE functions in meristem maintenance and flower development remains mysterious. Here, we show that the partial loss-of-function mutant of SE (se-1) shows additional floral organs and enlarged SAM sizes, and could restore FM activity in the stm mutant. We further demonstrate that SE represses the expression of STM-targeted KNOTTED-LIKE FROM ARABIDOPSIS THALIANA 2 (KNAT2) through miR171c-5p, thereby inhibiting the expression of ISOPENTENYL TRANSFERASE 7 (IPT7), which is activated by STM and is required for cytokinin biosynthesis. IPT7 can also be repressed by SE through the miR164c-CUP-SHAPED COTYLEDON 1/2 (CUC1/2)-KNAT2 regulatory module. Thus, FM activity promoted by restored cytokinin signaling could restore carpel formation in the se stm double mutant. The antagonistic regulation between SE and STM for FM maintenance ensures proper carpel development in Arabidopsis.

The histone acetyltransferase (HAT) GENERAL CONTROL NON DEREPRESSIBLE5 (GCN5) participates in various developmental processes in Arabidopsis (Arabidopsis thaliana). Notably, GCN5 ensures proper flower development, but the underlying mechanism remains unknown. Here, we show that during early flower development, GCN5 catalyzes histone acetylation at WUSCHEL (WUS) and CLAVATA3 (CLV3) chromatin, activating their expression. WUS and CLV3 are required for floral meristem (FM) maintenance. Furthermore, we demonstrate that the GCN5-ALTERATION/DEFICIENCY IN ACTIVATION 2 (ADA2) HAT module interacts with the Switch/Sucrose non-fermentable ATPase SPLAYED (SYD) to form a GCN5-ADA2b-SYD ternary complex. The cytokinin-responsive type-B Arabidopsis response regulators recruit this ternary complex for WUS activation. During floral organogenesis, PERIANTHIA recruits the GCN5-ADA2b module for AGAMOUS activation, which promotes FM determinacy. GCN5 also activates KNUCKLES, which ensures the timely termination of FM activity. Moreover, GCN5 modulates the expression pattern of the B-class gene APETALA3 and promotes the expression of SUPERMAN and CRABS CLAW, which are required for FM determinacy, thereby safeguarding meristem determinacy and correct floral organ formation. Thus, our study demonstrates the indispensable role of GCN5 in establishing a permissive chromatin environment to regulate the key genes required for precise flower development.

Meiosis produces haploid gametes that are essential for sexual reproduction in most eukaryotes, but the specific cell-cycle regulation that controls meiotic progression in plants remains to be fully characterized. KNUCKLES (KNU), a known transcriptional repressor in floral meristem regulation, also regulates anther development. Loss of KNU function leads to male sterility in Arabidopsis, but its detailed regulatory mechanism is unknown. Here, we find that KNU is specifically localized in meiocytes during anther development, and mutation of KNU disrupts meiotic progression and behavior, leading to apoptosis of microsporocytes. Transcriptome analysis shows that numerous genes related to meiosis are downregulated in knu-2 meiocytes. We demonstrate that KNU can directly repress the expression of two cell-cycle inhibitors, INTERACTOR/INHIBITOR OF CDK 1/KIP-RELATED PROTEIN 1 (ICK1/KRP1) and KRP3, and knockout of KRP1 or KRP3 in the null allele knu-2 background largely rescues the knu-2 defects in male meiosis and fertility. Consistent with these results, overexpression of KRP1 driven by the native KNU promoter results in meiotic defects and reduced expression of some meiosis-related genes, similar to the phenotypes of knu-2. Thus, our findings provide evidence that the transcription factor KNU regulates the expression of meiotic cell-cycle regulators and cohesins through suppression of KRP1/3, significantly broadening our understanding of plant meiosis.

Lateral root (LR) formation is governed by a complex regulatory network that includes various internal factors such as transcription factors (TFs) and phytohormones, of which ethylene is a key repressor. However, the core TFs that regulate ethylene biosynthesis and LR development remain unknown. Here, we found that the WRKY TF SbWRKY50 was required for LR development in Sorghum bicolour L. Overexpression of SbWRKY50 in sorghum increased the number and length of LRs, whereas both decreased in the CRISPR/Cas9-edited SbWRKY50 mutant. SbWRKY50 positively regulated LR generation by directly repressing several 1-aminocyclopropane-1-carboxylate synthase (ACS) genes. In addition, SbWRKY50 directly interacted with SbBMI1A to facilitate the recruitment of the PRC1 complex and induced H2A ubiquitination (H2Aub) accumulation on SbACS genes, thereby promoting epigenetic silencing and LR formation. The positive role of SbWRKY50 in stay-green and LR formation improves the agronomic traits of sorghum, improving drought tolerance and potentially contributing to increased sorghum yield.

SERRATE (SE) plays an important role in many biological processes and under biotic stress resistance. However, little about the control of SE has been clarified. Here we present a method named native chromatin-associated proteome affinity by CRISPR-dCas9 (CASPA-dCas9) to holistically capture native regulators of the SE locus. Several key regulatory factors including PHYTOCHROME RAPIDLY REGULATED 2 (PAR2), WRKY DNA-binding protein 19 (WRKY19) and the MYB-family protein MYB27 of SE are identified. MYB27 recruits the long non-coding RNA-PRC2 (SEAIR-PRC2) complex for H3K27me3 deposition on exon 1 of SE and subsequently represses SE expression, while PAR2-MYB27 interaction inhibits both the binding of MYB27 on the SE promoter and the recruitment of SEAIR-PRC2 by MYB27. The interaction between PAR2 and MYB27 fine-tunes the SE expression level at different developmental stages. In addition, PAR2 and WRKY19 synergistically promote SE expression for pathogen resistance. Collectively, our results demonstrate an efficient method to capture key regulators of target genes and uncover the precise regulatory mechanism for SE.

Contactin-2 (CNTN2), an immunoglobulin cell adhesion molecule (IgCAM) expressed on the neural cell surface, regulates the formation of myelin sheaths, facilitates communication between neurons and axoglial cells, and coordinates the migration of neural cells. However, the assembly of full-length CNTN2 is still not fully elucidated. Here, we found that the full-length human CNTN2 forms a concentration-dependent homodimer. We further determined the cryo-EM structures of the full-length CNTN2, revealing a novel bowknot-shaped scaffold constituted of the Ig1-6 repeats from two protomers, with the flexible ribbon-like FNIII repeats extending outward in opposite directions. The Ig1-6 domains, rather than the previously proposed Ig1-4 domains, have an indispensable role in mediating CNTN2-dependent cell adhesion and clustering. Moreover, structure-guided mutagenesis analyses supported the idea that CNTN2 homodimerization observed in our structure is essential for cell adhesion. Our findings offer novel insights into the mechanism through which CNTN2 forms a homodimer to maintain cell-cell contacts in the nervous system.

The onset of leaf de-greening and senescence is governed by a complex regulatory network including environmental cues and internal factors such as transcription factors (TFs) and phytohormones, in which ethylene (ET) is one key inducer. However, the detailed mechanism of ET signalling for senescence regulation is still largely unknown. Here, we found that the WRKY TF SbWRKY50 from Sorghum bicolor L., a direct target of the key component ETHYLENE INSENSITIVE 3 in ET signalling, functioned for leaf senescence repression. The clustered regularly interspaced short palindromic repeats/CRISPR-associated protein9-edited SbWRKY50 mutant (SbWRKY5O-KO) of sorghum displayed precocious senescent phenotypes, while SbWRKY50 overexpression delayed age-dependent and dark-induced senescence in sorghum. SbWRKY50 negatively regulated chlorophyll degradation through direct binding to the promoters of several chlorophyll catabolic genes. In addition, SbWRKY50 recruited the Polycomb repressive complex 1 through direct interaction with SbBMI1A, to induce histone 2A mono-ubiquitination accumulation on the chlorophyll catabolic genes for epigenetic silencing and thus delayed leaf senescence. Especially, SbWRKY50 can suppress early steps of chlorophyll catabolic pathway via directly repressing SbNYC1 (NON-YELLOW COLORING 1). Other senescence-related hormones could also influence leaf senescence through repression of SbWRKY50. Hence, our work shows that SbWRKY50 is an essential regulator downstream of ET and SbWRKY50 also responds to other phytohormones for senescence regulation in sorghum.

SERRATE (SE) is a core protein for microRNA (miRNA) biogenesis as well as for mRNA alternative splicing. Investigating the regulatory mechanism of SE expression is hence critical to understanding its detailed function in diverse biological processes. However, little about the control of SE expression has been clarified, especially through long noncoding RNA (lncRNA). Here, we identified an antisense intragenic lncRNA transcribed from the 3' end of SE, named SEAIRa. SEAIRa repressed SE expression, which in turn led to serrated leaves. SEAIRa recruited plant U-box proteins PUB25/26 with unreported RNA binding ability and a ubiquitin-like protein related to ubiquitin 1 (RUB1) for H2A monoubiquitination (H2Aub) at exon 11 of SE. In addition, PUB25/26 helped cleave SEAIRa and release the 5' domain fragment, which recruited the PRC2 complex for H3 lysine 27 trimethylation (H3K27me3) deposition at the first exon of SE. The distinct modifications of H2Aub and H3K27me3 at different sites of the SE locus cooperatively suppressed SE expression. Collectively, our results uncover an epigenetic mechanism mediated by the lncRNA SEAIRa that modulates SE expression, which is indispensable for plant growth and development.

20世纪60年代初,英国的麦克米伦政府就双边核合作议题同法国的戴高乐政府进行外交接触,接触主要是通过双边会议渠道展开的,但双方的接触没有获得任何实质性成果。造成双方接触无果而终的主要原因在于双方对"独立核力量"的不同认知、美国的极力反对以及麦克米伦内阁里反对英法进行核合作的阁员的阻挠。