The APC/CTE E3 Ubiquitin Ligase Complex Mediates the Antagonistic Regulation of Root Growth and Tillering by ABA and GA

Effect of Combined Urea and Calcium Nitrate Application on Wheat Tiller Development, Nitrogen Use Efficiency, and Grain Yield

Optimizing nitrogen (N) sources has the potential to improve wheat tillering, nitrogen use efficiency (NUE), and grain yield, yet the underlying mechanisms remain unclear. This study hypothesizes that combining specific N sources can increase zeatin riboside + zeatin (ZR + ZT) content in tiller nodes and maintain a higher ZR + ZT/gibberellin A7 (GA7) ratio, thereby promoting tiller development, enhancing NUE, and increasing yield. The effects of N source treatments on two wheat cultivars, the multi-spike Shannong 28 (SN28) and the large-spike Tainong 18 (TN18), were investigated. A total of seven N treatments were tested: no nitrogen (N0), urea (N1), calcium nitrate (N2), ammonium chloride (N3), and equal doses of urea and calcium nitrate (N4), urea and ammonium chloride (N5), and calcium nitrate and ammonium chloride (N6). The results showed that treatment N4 significantly increased the levels of ZR and ZT in tiller nodes, while maintaining a higher ZR + ZT to GA7 ratio. This hormonal shift promoted tiller formation and biomass accumulation. Under N4, both cultivars exhibited the highest number of effective spikes and biomass in higher-order tillers. N4 also enhanced N accumulation in the grains, N absorption efficiency, and N translocation, while reducing N loss. Compared to N1, effective spike numbers increased by 7.8% in SN28 and 5.6% in TN18, resulting in a 6.4% increase in grain yield for SN28 and a 2.2% increase for TN18. In conclusion, the combined application of urea and calcium nitrate optimizes hormonal regulation, improves NUE, and significantly enhances wheat tillering and grain yield, providing a promising strategy for enhancing wheat productivity.

TavWA1 is critical for wheat growth by modulating cell morphology and arrangement

Plant growth is determined by the production of cells and initiation of new organs. Exploring genes that control cell number and cell size is of great significance for understanding plant growth regulation. In this study, we characterized two wheat mutants, ah and dl, with abnormal growth. The ah mutant is a naturally occurring variant characterized by severe dwarfism, increased tiller number, and reduced grain length, while the dl mutant is derived from an ethyl methane sulfonate (EMS)-mutagenized population and exhibits smaller grain size and slightly reduced plant height. Cytological analyses revealed abnormal cell number, cell morphology and arrangement in the stems and leaves of the ah mutant, along with reduced cell length in the grains of the dl mutant. Map-based cloning identified that both mutants carry mutations in the same gene TavWA1-7D, which encodes a protein with a von Willebrand factor A (vWA) domain. The ah mutant harbors a 174-bp insertion in the 1,402-bp coding sequence (CDS) of TavWA1-7D, causing premature termination of protein translation, while the dl mutant contains a Glu420Lys substitution. Mimicking the TavWA1-7Dah through clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease 9-mediated genome editing leads to a severe dwarfism phenotype. The C-terminus of the protein is crucial for its correct subcellular localization and interaction, supporting its critical role for TavWA1-7D function. Proteomic analysis showed that the dwarf phenotype of the ah mutant is associated with impaired photosynthesis, ribosome function, and nucleosome formation. Additionally, TavWA1-7D interacts with an E3 ligase, TaVIP1-3B, the expression levels of which are elevated in both mutants. Overexpression and knockout studies of TaVIP1-3B demonstrated its negative regulatory role in cell length and grain size. Together, our findings suggest that TavWA1-7D plays a vital role in regulating wheat growth and yield-related traits, with the dl mutant's short grain phenotype being associated with TaVIP1-3B expression levels.

Regulation of tillering and panicle branching in rice and wheat

Branching is a critical aspect of plant architecture that significantly impacts the yield and adaptability of staple cereal crops like rice and wheat. Cereal crops develop tillers during the vegetative stage and panicle or spike branches during the reproductive stage, respectively, both of which are significantly impacted by hormones and genetic factors. Tillering and panicle branching are closely interconnected and exhibit high environmental plasticity. Here, we summarize the recent progress in genetic, hormonal, and environmental factors regulation in the branching of rice and wheat. This review not only provides a comprehensive overview of the current knowledge on branching mechanisms in rice and wheat, but also explores the prospects for future research aimed at optimizing crop architecture for enhanced productivity.

MaMPK19, a key gene enhancing cold resistance by activating the CBF pathway in banana

MPKs play an essential part role in the process of plant low temperature stress. In this study, the specific inhibitor SB203580 of MPK was used to spray banana leaves and MaMPK19 was overexpressed in N.benthamiana and banana to explore the effect of MaMPK19 on cold resistance and the regulation mode of downstream genes. Additionally, we optimized the method of genetic transformation of banana laying the foundation for the establishment of an efficient genetic transformation system. The results showed that 40 μmol L-1 SB203580 could significantly reduce the expression of MaMPK19 and MaCBFs, as well as weaken the cold resistance of banana at 4 °C. After agrobacterium tumefaciens infection, the regeneration rates of adventitious buds in 'Tianbao', 'Brazilian' and'Indonesia' (Musa spp. AAA Group, Cavendish) reached 10.43%, 15.81% and 14.23%, respectively. And the positive rates reached 10.71%, 2.25% and 6.94%, respectively. Overexpression of MaMPK19 enhanced the cold resistance of N.benthamiana and bananas. MaMPK19 promoted the expression of MaICE1, MaDREB1D and MaCOR413. Furthermore, MaMPK19 increased POD activity and the content of ABA and JA. Our study highlights the importance of MaMPK19 in improving the cold resistance of bananas and provides a reference for biological breeding.

The BnaBPs gene regulates flowering time and leaf angle in Brassica napus

The flowering time and plant architecture of Brassica napus were significantly associated with yield. In this study, we found that the BREVIPEDICELLUS/KNAT1(BP) gene regulated the flowering time and plant architecture of B. napus. However, the precise regulatory mechanism remains unclear. We cloned two homologous BP genes, BnaBPA03 and BnaBPC03, from B. napus Xiaoyun. The protein sequence analysis showed two proteins containing conserved domains KNOX I, KNOX II, ELK, and HOX of the KONX protein family. The CRISPR/Cas9 knockout lines exhibited early budding and flowering time, coupled with floral organ abscission earlier and a larger leaf angle. On the contrary, overexpression plants displayed a phenotype that was the inverse of these characteristics. Furthermore, we observed upregulation of gibberellin and ethylene biosynthesis genes, as well as floral integrator genes in knocked-out plants. The results revealed that BnaBPs play a role in flowering time, floral organ abscission, and leaf angle as well as germination processes mediated. Additionally, BnaBPs exerted an impact on the biosynthesis pathways of ethylene and GA.

Loss of Lateral suppressor gene is associated with evolution of root nodule symbiosis in Leguminosae

BACKGROUND

Root nodule symbiosis (RNS) is a fascinating evolutionary event. Given that limited genes conferring the evolution of RNS in Leguminosae have been functionally validated, the genetic basis of the evolution of RNS remains largely unknown. Identifying the genes involved in the evolution of RNS will help to reveal the mystery.

RESULTS

Here, we investigate the gene loss event during the evolution of RNS in Leguminosae through phylogenomic and synteny analyses in 48 species including 16 Leguminosae species. We reveal that loss of the Lateral suppressor gene, a member of the GRAS-domain protein family, is associated with the evolution of RNS in Leguminosae. Ectopic expression of the Lateral suppressor (Ls) gene from tomato and its homolog MONOCULM 1 (MOC1) and Os7 from rice in soybean and Medicago truncatula result in almost completely lost nodulation capability. Further investigation shows that Lateral suppressor protein, Ls, MOC1, and Os7 might function through an interaction with NODULATION SIGNALING PATHWAY 2 (NSP2) and CYCLOPS to repress the transcription of NODULE INCEPTION (NIN) to inhibit the nodulation in Leguminosae. Additionally, we find that the cathepsin H (CTSH), a conserved protein, could interact with Lateral suppressor protein, Ls, MOC1, and Os7 and affect the nodulation.

CONCLUSIONS

This study sheds light on uncovering the genetic basis of the evolution of RNS in Leguminosae and suggests that gene loss plays an essential role.

Effect of Nutrient Solution Flow on Lettuce Root Morphology in Hydroponics: A Multi-Omics Analysis of Hormone Synthesis and Signal Transduction

This study examined how the nutrient flow environment affects lettuce root morphology in hydroponics using multi-omics analysis. The results indicate that increasing the nutrient flow rate initially increased indicators such as fresh root weight, root length, surface area, volume, and average diameter before declining, which mirrors the trend observed for shoot fresh weight. Furthermore, a high-flow environment significantly increased root tissue density. Further analysis using Weighted Gene Co-expression Network Analysis (WGCNA) and Weighted Protein Co-expression Network Analysis (WPCNA) identified modules that were highly correlated with phenotypes and hormones. The analysis revealed a significant enrichment of hormone signal transduction pathways. Differences in the expression of genes and proteins related to hormone synthesis and transduction pathways were observed among the different flow conditions. These findings suggest that nutrient flow may regulate hormone levels and signal transmission by modulating the genes and proteins associated with hormone biosynthesis and signaling pathways, thereby influencing root morphology. These findings should support the development of effective methods for regulating the flow of nutrients in hydroponic contexts.

Transcription factor OsSHR2 regulates rice architecture and yield per plant in response to nitrogen

MAIN CONCLUSION

Mutation of OsSHR2 adversely impacted root and shoot growth and impaired plant response to N conditions, further reducing the yield per plant. Nitrogen (N) is a crucial factor that regulates the plant architecture. There is still a lack of research on it. In our study, it was observed that the knockout of the SHORTROOT 2 (OsSHR2) which was induced by N deficiency, can significantly affect the regulation of plant architecture response to N in rice. Under N deficiency, the mutation of OsSHR2 significantly reduced root growth, and impaired the sensitivity of the root meristem length to N deficiency. The mutants were found to have approximately a 15% reduction in plant height compared to wild type. But mutants showed a significant increase in tillering at post-heading stage, approximately 26% more than the wild type, particularly in high N conditions. In addition, due to reduced seed setting rate and 1000-grain weight, mutant yield was significantly decreased by approximately 33% under low N fertilizer supply. The mutation also changed the distribution of N between the vegetative and reproductive organs. Our findings suggest that the transcription factor OsSHR2 plays a regulatory role in the response of plant architecture and yield per plant to N in rice.

The ABI4-RGL2 module serves as a double agent to mediate the antagonistic crosstalk between ABA and GA signals

Abscisic acid (ABA) and gibberellins (GA) antagonistically mediate several biological processes, including seed germination, but the molecular mechanisms underlying ABA/GA antagonism need further investigation, particularly any role mediated by a transcription factors module. Here, we report that the DELLA protein RGL2, a repressor of GA signaling, specifically interacts with ABI4, an ABA signaling enhancer, to act as a transcription factor complex to mediate ABA/GA antagonism. The rgl2, abi3, abi4 and abi5 mutants rescue the non-germination phenotype of the ga1-t. Further, we demonstrate that RGL2 specifically interacts with ABI4 to form a heterodimer. RGL2 and ABI4 stabilize one another, and GA increases the ABI4-RGL2 module turnover, whereas ABA decreases it. At the transcriptional level, ABI4 enhances the RGL2 expression by directly binding to its promoter via the CCAC cis-element, and RGL2 significantly upregulates the transcriptional activation ability of ABI4 toward its target genes, including ABI5 and RGL2. Abscisic acid promotes whereas GA inhibits the ability of ABI4-RGL2 module to activate transcription, and ultimately ABA and GA antagonize each other. Genetic analysis demonstrated that both ABI4 and RGL2 are essential for the activity of this transcription factor module. These results suggest that the ABI4-RGL2 module mediates ABA/GA antagonism by functioning as a double agent.

Genome-Wide Identification and Analysis of APC E3 Ubiquitin Ligase Genes Family in Triticum aestivum

E3 ubiquitin ligases play a pivotal role in ubiquitination, a crucial post-translational modification process. Anaphase-promoting complex (APC), a large cullin-RING E3 ubiquitin ligase, regulates the unidirectional progression of the cell cycle by ubiquitinating specific target proteins and triggering plant immune responses. Several E3 ubiquitin ligases have been identified owing to advancements in sequencing and annotation of the wheat genome. However, the types and functions of APC E3 ubiquitin ligases in wheat have not been reported. This study identified 14 members of the APC gene family in the wheat genome and divided them into three subgroups (CCS52B, CCS52A, and CDC20) to better understand their functions. Promoter sequence analysis revealed the presence of several cis-acting elements related to hormone and stress responses in the APC E3 ubiquitin ligases in wheat. All identified APC E3 ubiquitin ligase family members were highly expressed in the leaves, and the expression of most genes was induced by the application of methyl jasmonate (MeJA). In addition, the APC gene family in wheat may play a role in plant defense mechanisms. This study comprehensively analyzes APC genes in wheat, laying the groundwork for future research on the function of APC genes in response to viral infections and expanding our understanding of wheat immunity mechanisms.

The GRAS protein OsDLA involves in brassinosteroid signalling and positively regulates blast resistance by forming a module with GSK2 and OsWRKY53 in rice

Brassinosteroids (BRs) play a crucial role in shaping the architecture of rice (Oryza sativa) plants. However, the regulatory mechanism of BR signalling in rice immunity remains largely unexplored. Here we identify a rice mutant dla, which exhibits decreased leaf angles and is insensitive to 24-epiBL (a highly active synthetic BR), resembling the BR-deficient phenotype. The dla mutation caused by a T-DNA insertion in the OsDLA gene leads to downregulation of the causative gene. The OsDLA knockout plants display reduced leaf angles and less sensitivity to 24-epiBL. In addition, both dla mutant and OsDLA knockout plants are more susceptible to rice blast compared to the wild type. OsDLA is a GRAS transcription factor and interacts with the BR signalling core negative regulator, GSK2. GSK2 phosphorylates OsDLA for degradation via the 26S proteasome. The GSK2 RNAi line exhibits enhanced rice blast resistance, while the overexpression lines thereof show susceptibility to rice blast. Furthermore, we show that OsDLA interacts with and stabilizes the WRKY transcription factor OsWRKY53, which has been demonstrated to positively regulate BR signalling and blast resistance. OsWRKY53 directly binds the promoter of PBZ1 and activates its expression, and this activation can be enhanced by OsDLA. Together, our findings unravel a novel mechanism whereby the GSK2-OsDLA-OsWRKY53 module coordinates blast resistance and plant architecture via BR signalling in rice.

All-Year High IAA and ABA Contents in Rhizome Buds May Contribute to Natural Four-Season Shooting in Woody Bamboo Cephalostachyum pingbianense

To explore the regulation mechanism of endogenous phytohormones on rhizome bud germination in Cephalostachyum pingbianense, the contents of IAA, ABA, GA, and CTK in seven above- and under-ground bamboo structure components were determined using enzyme-linked immunosorbent assays (ELISA). The results showed that a higher content of IAA, GA, and CTK all year was found in above-ground components and dormant rhizome buds. Meanwhile, a higher ABA content in young shoots and a lower ABA content in the culm base and dormant rhizome buds were detected during the peak period of shooting. The amounts of emerging shoots and the grown bamboo culms were positively correlated with the content of IAA and the ratio of IAA/ABA and (IAA + CTK + GA)/ABA, while they were negatively correlated with the ratio of CTK/IAA in dormant rhizome buds. The all-year high contents of IAA (19-31 ng/g) and ABA (114-144 ng/g) in rhizome buds, as well as interactions among four hormones, may be the key physiological mechanisms to maintain rhizome bud germination throughout the year in C. pingbianense. As C. pingbianense is a special bamboo species of multi-season shoot sprouting, the above results may supplement scientific data for a comprehensive understanding of physiological mechanisms within the bamboo subfamily.

GRAS family member LATERAL SUPPRESSOR regulates the initiation and morphogenesis of watermelon lateral organs

The lateral organs of watermelon (Citrullus lanatus), including lobed leaves, branches, flowers, and tendrils, together determine plant architecture and yield. However, the genetic controls underlying lateral organ initiation and morphogenesis remain unclear. Here, we found that knocking out the homologous gene of shoot branching regulator LATERAL SUPPRESSOR in watermelon (ClLs) repressed the initiation of branches, flowers, and tendrils and led to developing round leaves, indicating that ClLs undergoes functional expansion compared with its homologs in Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and tomato (Solanum lycopersicum). Using ClLs as the bait to screen against the cDNA library of watermelon, we identified several ClLs-interacting candidate proteins, including TENDRIL (ClTEN), PINOID (ClPID), and APETALA1 (ClAP1). Protein-protein interaction assays further demonstrated that ClLs could directly interact with ClTEN, ClPID, and ClAP1. The mRNA in situ hybridization assay revealed that the transcriptional patterns of ClLs overlapped with those of ClTEN, ClPID, and ClAP1 in the axillary meristems and leaf primordia. Mutants of ClTEN, ClPID, and ClAP1 generated by the CRISPR/Cas9 gene editing system lacked tendrils, developed round leaves, and displayed floral diapause, respectively, and all these phenotypes could be observed in ClLs knockout lines. Our findings indicate that ClLs acts as lateral organ identity protein by forming complexes with ClTEN, ClPID, and ClAP1, providing several gene targets for transforming the architecture of watermelon.

Coordination of growth and drought responses by GA-ABA signaling in rice

The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought stress, energy and resources should be diverted from growth toward stress management. However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive. Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co-activator of anaphase-promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance. These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance.

Transcriptomic analysis implicates ABA signaling and carbon supply in the differential outgrowth of petunia axillary buds

BACKGROUND

Shoot branching of flowering plants exhibits phenotypic plasticity and variability. This plasticity is determined by the activity of axillary meristems, which in turn is influenced by endogenous and exogenous cues such as nutrients and light. In many species, not all buds on the main shoot develop into branches despite favorable growing conditions. In petunia, basal axillary buds (buds 1-3) typically do not grow out to form branches, while more apical axillary buds (buds 6 and 7) are competent to grow.

RESULTS

The genetic regulation of buds was explored using transcriptome analyses of petunia axillary buds at different positions on the main stem. To suppress or promote bud outgrowth, we grew the plants in media with differing phosphate (P) levels. Using RNA-seq, we found many (> 5000) differentially expressed genes between bud 6 or 7, and bud 2. In addition, more genes were differentially expressed when we transferred the plants from low P to high P medium, compared with shifting from high P to low P medium. Buds 6 and 7 had increased transcript abundance of cytokinin and auxin-related genes, whereas the basal non-growing buds (bud 2 and to a lesser extent bud 3) had higher expression of strigolactone, abscisic acid, and dormancy-related genes, suggesting the outgrowth of these basal buds was actively suppressed. Consistent with this, the expression of ABA associated genes decreased significantly in apical buds after stimulating growth by switching the medium from low P to high P. Furthermore, comparisons between our data and transcriptome data from other species suggest that the suppression of outgrowth of bud 2 was correlated with a limited supply of carbon to these axillary buds. Candidate genes that might repress bud outgrowth were identified by co-expression analysis.

CONCLUSIONS

Plants need to balance growth of axillary buds into branches to fit with available resources while allowing some buds to remain dormant to grow after the loss of plant parts or in response to a change in environmental conditions. Here we demonstrate that different buds on the same plant with different developmental potentials have quite different transcriptome profiles.

Wheat gibberellin oxidase genes and their functions in regulating tillering

Multiple genetic factors control tillering, a key agronomy trait for wheat (Triticum aestivum L.) yield. Previously, we reported a dwarf-monoculm mutant (dmc) derived from wheat cultivar Guomai 301, and found that the contents of gibberellic acid 3 (GA3) in the tiller primordia of dmc were significantly higher. Transcriptome analysis indicated that some wheat gibberellin oxidase (TaGAox) genes TaGA20ox-A2, TaGA20ox-B2, TaGA3ox-A2, TaGA20ox-A4, TaGA2ox-A10 and TaGA2ox-B10 were differentially expressed in dmc. Therefore, this study systematically analyzed the roles of gibberellin oxidase genes during wheat tillering. A total of 63 TaGAox genes were identified by whole genome analysis. The TaGAoxs were clustered to four subfamilies, GA20oxs, GA2oxs, GA3oxs and GA7oxs, including seven subgroups based on their protein structures. The promoter regions of TaGAox genes contain a large number of cis-acting elements closely related to hormone, plant growth and development, light, and abiotic stress responses. Segmental duplication events played a major role in TaGAoxs expansion. Compared to Arabidopsis, the gene collinearity degrees of the GAoxs were significantly higher among wheat, rice and maize. TaGAox genes showed tissue-specific expression patterns. The expressions of TaGAox genes (TaGA20ox-B2, TaGA7ox-A1, TaGA2ox10 and TaGA3ox-A2) were significantly affected by exogenous GA3 applications, which also significantly promoted tillering of Guomai 301, but didn't promote dmc. TaGA7ox-A1 overexpression transgenic wheat lines were obtained by Agrobacterium mediated transformation. Genomic PCR and first-generation sequencing demonstrated that the gene was integrated into the wheat genome. Association analysis of TaGA7ox-A1 expression level and tiller number per plant demonstrated that the tillering capacities of some TaGA7ox-A1 transgenic lines were increased. These data demonstrated that some TaGAoxs as well as GA signaling were involved in regulating wheat tillering, but the GA signaling pathway was disturbed in dmc. This study provided valuable clues for functional characterization of GAox genes in wheat.

Characterization of the Molecular Events Underlying the Establishment of Axillary Meristem Region in Pepper

Plant architecture is a major motif of plant diversity, and shoot branching patterns primarily determine the aerial architecture of plants. In this study, we identified an inbred pepper line with fewer lateral branches, 20C1734, which was free of lateral branches at the middle and upper nodes of the main stem with smooth and flat leaf axils. Successive leaf axil sections confirmed that in normal pepper plants, for either node n, Pn (Primordium n) < 1 cm and Pn+1 < 1 cm were the critical periods between the identification of axillary meristems and the establishment of the region, whereas Pn+3 < 1 cm was fully developed and formed a completely new organ. In 20C1734, the normal axillary meristematic tissue region establishment and meristematic cell identity confirmation could not be performed on the axils without axillary buds. Comparative transcriptome analysis revealed that "auxin-activated signaling pathway", "response to auxin", "response to abscisic acid", "auxin biosynthetic process", and the biosynthesis of the terms/pathways, such as "secondary metabolites", were differentially enriched in different types of leaf axils at critical periods of axillary meristem development. The accuracy of RNA-seq was verified using RT-PCR for some genes in the pathway. Several differentially expressed genes (DEGs) related to endogenous phytohormones were targeted, including several genes of the PINs family. The endogenous hormone assay showed extremely high levels of IAA and ABA in leaf axils without axillary buds. ABA content in particular was unusually high. At the same time, there is no regular change in IAA level in this type of leaf axils (normal leaf axils will be accompanied by AM formation and IAA content will be low). Based on this, we speculated that the contents of endogenous hormones IAA and ABA in 20C1734 plant increased sharply, which led to the abnormal expression of genes in related pathways, which affected the formation of Ams in leaf axils in the middle and late vegetative growth period, and finally, nodes without axillary buds and side branches appeared.

PROTEIN PHOSPHATASE 2C08, a Negative Regulator of Abscisic Acid Signaling, Promotes Internode Elongation in Rice

Clade A protein phosphatase 2Cs (PP2CAs) negatively regulate abscisic acid (ABA) signaling. Here, we investigated the functions of OsPP2CAs and their crosstalk with ABA and gibberellic acid (GA) signaling pathways in rice (Oryza sativa). Among the nine OsPP2CAs, OsPP2C08 had the highest amino acid sequence similarity with OsPP2C51, which positively regulates GA signaling in rice seed germination. However, OsPP2C08 was expressed in different tissues (internodes, sheaths, and flowers) compared to OsPP2C51, which was specifically expressed in seeds, and showed much stronger induction under abiotic stress than OsPP2C51. Transgenic rice lines overexpressing OsPP2C08 (OsPP2C08-OX) had a typical ABA-insensitive phenotype in a post-germination assay, indicating that OsPP2C08, as with other OsPP2CAs, negatively regulates ABA signaling. Furthermore, OsPP2C08-OX lines had longer stems than wild-type (WT) plants due to longer internodes, especially between the second and third nodes. Internode cells were also longer in OsPP2C08-OX lines than in the WT. As GA positively regulates plant growth, these results suggest that OsPP2C08 might positively regulate GA biosynthesis. Indeed, the expression levels of GA biosynthetic genes including gibberellin 20-oxidase (OsGA20ox4) and Ent-kaurenoic acid oxidase (OsKAO) were increased in OsPP2C08-OX lines, and we observed that GIBBERELLIN 2-OXIDASE 4 (OsGA2ox4), encoding an oxidase that catalyzes the 2-beta-hydroxylation of several biologically active GAs, was repressed in the OsPP2C08-OX lines based on a transcriptome deep sequencing and RT-qPCR analysis. Furthermore, we compared the accumulation of SLENDER RICE 1 (SLR1), a DELLA protein involved in GA signaling, in OsPP2C08-OX and WT plants, and observed lower levels of SLR1 in the OsPP2C08-OX lines than in the WT. Taken together, our results reveal that OsPP2C08 negatively regulates ABA signaling and positively regulates GA signaling in rice. Our study provides valuable insight into the molecular mechanisms underlying the crosstalk between GA and ABA signaling in rice.

RRS1 shapes robust root system to enhance drought resistance in rice

A strong root system facilitates the absorption of water and nutrients from the soil, to improve the growth of crops. However, to date, there are still very few root development regulatory genes that can be used in crop breeding for agriculture. In this study, we cloned a negative regulator gene of root development, Robust Root System 1 (RRS1), which encodes an R2R3-type MYB family transcription factor. RRS1 knockout plants showed enhanced root growth, including longer root length, longer lateral root length, and larger lateral root density. RRS1 represses root development by directly activating the expression of OsIAA3 which is involved in the auxin signaling pathway. A natural variation in the coding region of RRS1 changes the transcriptional activity of its protein. RRS1^T allele, originating from wild rice, possibly increases root length by means of weakening regulation of OsIAA3. Knockout of RRS1 enhances drought resistance by promoting water absorption and improving water use efficiency. This study provides a new gene resource for improving root systems and cultivating drought-resistant rice varieties with important values in agricultural applications.

Plant lineage-specific PIKMIN1 drives APC/CCCS52A2 E3-ligase activity-dependent cell division

The anaphase-promoting complex/cyclosome (APC/C) marks key cell cycle proteins for proteasomal breakdown, thereby ensuring unidirectional progression through the cell cycle. Its target recognition is temporally regulated by activating subunits, one of which is called CELL CYCLE SWITCH 52 A2 (CCS52A2). We sought to expand the knowledge on the APC/C by using the severe growth phenotypes of CCS52A2-deficient Arabidopsis (Arabidopsis thaliana) plants as a readout in a suppressor mutagenesis screen, resulting in the identification of the previously undescribed gene called PIKMIN1 (PKN1). PKN1 deficiency rescues the disorganized root stem cell phenotype of the ccs52a2-1 mutant, whereas an excess of PKN1 inhibits the growth of ccs52a2-1 plants, indicating the need for control of PKN1 abundance for proper development. Accordingly, the lack of PKN1 in a wild-type background negatively impacts cell division, while its systemic overexpression promotes proliferation. PKN1 shows a cell cycle phase-dependent accumulation pattern, localizing to microtubular structures, including the preprophase band, the mitotic spindle, and the phragmoplast. PKN1 is conserved throughout the plant kingdom, with its function in cell division being evolutionarily conserved in the liverwort Marchantia polymorpha. Our data thus demonstrate that PKN1 represents a novel, plant-specific protein with a role in cell division that is likely proteolytically controlled by the CCS52A2-activated APC/C.

Abscisic acid and its role in the modulation of plant growth, development, and yield stability

Abscisic acid (ABA) is known to confer stress tolerance; however, at elevated levels it impairs plant growth under prolonged stress. Paradoxically, at its basal level, ABA plays many vital roles in promoting plant growth and development, including modulation of tillering, flowering, and seed development, as well as seed maturation. In this review, we provide insight into novel discoveries of ABA fluxes, ABA signaling responses, and their impact on yield stability. We discuss ABA homeostasis implicated under pre- and postanthesis drought and its impact on productive tillers, grain number determination, and seed development to address yield stability in cereal crops while considering the new knowledge that emerged from the model plant systems.

Knockdown of NtCPS2 promotes plant growth and reduces drought tolerance in Nicotiana tabacum

Drought stress is one of the primary environmental stress factors that gravely threaten crop growth, development, and yields. After drought stress, plants can regulate the content and proportion of various hormones to adjust their growth and development, and in some cases to minimize the adverse effects of drought stress. In our previous study, the tobacco cis-abienol synthesis gene (NtCPS2) was found to affect hormone synthesis in tobacco plants. Unfortunately, the role of NtCPS2 genes in the response to abiotic stress has not yet been investigated. Here, we present data supporting the role of NtCPS2 genes in drought stress and the possible underlying molecular mechanisms. NtCPS2 gene expression was induced by polyethylene glycol, high-temperature, and virus treatments. The results of subcellular localization showed that NtCPS2 was localized in the cell membrane. The NtCPS2-knockdown plants exhibited higher levels of gibberellin (GA) content and synthesis pathway genes expression but lower abscisic acid (ABA) content and synthesis pathway genes expression in response to drought stress. In addition, the transgenic tobacco lines showed higher leaf water loss and electrolyte loss, lower soluble protein and reactive oxygen species content (ROS), and lower antioxidant enzyme activity after drought treatment compared to wild type plants (WT). In summary, NtCPS2 positively regulates drought stress tolerance possibly by modulating the ratio of GA to ABA, which was confirmed by evidence of related phenotypic and physiological indicators. This study may provide evidence for the feedback regulation of hormone to abiotic and biotic stresses.

The APC/CTAD1-WIDE LEAF 1-NARROW LEAF 1 pathway controls leaf width in rice

Leaf morphology is one of the most important features of the ideal plant architecture. However, the genetic and molecular mechanisms controlling this feature in crops remain largely unknown. Here, we characterized the rice (Oryza sativa) wide leaf 1 (wl1) mutant, which has wider leaves than the wild-type due to more vascular bundles and greater distance between small vascular bundles. WL1 encodes a Cys-2/His-2-type zinc finger protein that interacts with Tillering and Dwarf 1 (TAD1), a co-activator of the anaphase-promoting complex/cyclosome (APC/C) (a multi-subunit E3 ligase). The APC/CTAD1 complex degrades WL1 via the ubiquitin-26S proteasome degradation pathway. Loss-of-function of TAD1 resulted in plants with narrow leaves due to reduced vascular bundle numbers and distance between the small vascular bundles. Interestingly, we found that WL1 negatively regulated the expression of a narrow leaf gene, NARROW LEAF 1 (NAL1), by recruiting the co-repressor TOPLESS-RELATED PROTEIN and directly binding to the NAL1 regulatory region to inhibit its expression by reducing the chromatin histone acetylation. Furthermore, biochemical and genetic analyses revealed that TAD1, WL1, and NAL1 operated in a common pathway to control the leaf width. Our study establishes an important framework for understanding the APC/CTAD1-WL1-NAL1 pathway-mediated control of leaf width in rice, and provides insights for improving crop plant architecture.

Joint metabolome and transcriptome analysis of the effects of exogenous GA3 on endogenous hormones in sweet cherry and mining of potential regulatory genes

Gibberellin (GA) is an important phytohormone that can participate in various developmental processes of plants. The study found that application of GA₃ can induce parthenocarpy fruit and improve fruit set. However, the use of GA₃ affects endogenous hormones in fruits, thereby affecting fruit quality. This study mainly investigates the effect of exogenous GA₃ on endogenous hormones in sweet cherries. The anabolic pathways of each hormone were analyzed by metabolome and transcriptome to identify key metabolites and genes that affect endogenous hormones in response to exogenous GA₃ application. Results showed that exogenous GA₃ led to a significant increase in the content of abscisic acid (ABA) and GA and affected jasmonic acid (JA) and auxin (IAA). At the same time, the key structural genes affecting the synthesis of various hormones were preliminarily determined. Combined with transcription factor family analysis, WRKY genes were found to be more sensitive to the use of exogenous GA₃, especially the genes belonging to Group III (PaWRKY16, PaWRKY21, PaWRKY38, PaWRKY52, and PaWRKY53). These transcription factors can combine with the promoters of NCED, YUCCA, and other genes to regulate the content of endogenous hormones. These findings lay the foundation for the preliminary determination of the mechanism of GA₃'s effect on endogenous hormones in sweet cherry and the biological function of WRKY transcription factors.

The role of APC/C in cell cycle dynamics, growth and development in cereal crops

Cereal crops can be considered the basis of human civilization. Thus, it is not surprising that these crops are grown in larger quantities worldwide than any other food supply and provide more energy to humankind than any other provision. Additionally, attempts to harness biomass consumption continue to increase to meet human energy needs. The high pressures for energy will determine the demand for crop plants as resources for biofuel, heat, and electricity. Thus, the search for plant traits associated with genetic increases in yield is mandatory. In multicellular organisms, including plants, growth and development are driven by cell division. These processes require a sequence of intricated events that are carried out by various protein complexes and molecules that act punctually throughout the cycle. Temporal controlled degradation of key cell division proteins ensures a correct onset of the different cell cycle phases and exit from the cell division program. Considering the cell cycle, the Anaphase-Promoting Complex/Cyclosome (APC/C) is an important conserved multi-subunit ubiquitin ligase, marking targets for degradation by the 26S proteasome. Studies on plant APC/C subunits and activators, mainly in the model plant Arabidopsis, revealed that they play a pivotal role in several developmental processes during growth. However, little is known about the role of APC/C in cereal crops. Here, we discuss the current understanding of the APC/C controlling cereal crop development.

Selection and Validation of 48 KASP Markers for Variety Identification and Breeding Guidance in Conventional and Hybrid Rice (Oryza sativa L.)

BACKGROUND

Breeding of conventional and hybrid rice (Oryza sativa L.) have solved hunger problems and increased farmers' income in the world. Molecular markers have been widely used in marker-assisted breeding and identification of larger numbers of different bred varieties in the past decades. The recently developed SNP markers are applied for more stable and detectable compared with other markers. But the cost of genotyping lots SNPs is high. So, it is essential to select less representative SNPs and inexpensive detecting methods to lower the cost and accelerate variety identification and breeding process. KASP (Kompetitive Allele-Specific PCR) is a flexible method to detect the SNPs, and large number of KASP markers have been widely used in variety identification and breeding. However, the ability of less KASP markers on massive variety identification and breeding remains unknown.

RESULTS

Here, 48 KASP markers were selected from 378 markers to classify and analyze 518 varieties including conventional and hybrid rice. Through analyzing the population structure, the 48 markers could almost represent the 378 markers. In terms of variety identification, the 48 KASP markers had a 100% discrimination rate in 53 conventional indica varieties and 193 hybrid varieties, while they could distinguish 89.1% conventional japonica rice from different breeding institutes. Two more markers added would increase the ratio from 68.38 to 77.94%. Additionally, the 48 markers could be used for classification of subpopulations in the bred variety. Also, 8 markers had almost completely different genotypes between japonica and indica, and 3 markers were found to be very important for japonica hybrid rice. In hybrid varieties, the heterozygosity of chromosomes 3, 6 and 11 was relatively higher than others.

CONCLUSIONS

Our results showed that 48 KASP markers could be used to identify rice varieties, and the panel we tested could provide a database for breeders to identify new breeding lines. Also, the specific markers we found were useful for marker-assisted breeding in rice, including conventional and hybrid.

E3 ligase AtAIRP5/GARU regulates drought stress response by stimulating SERINE CARBOXYPEPTIDASE-LIKE1 turnover

Ubiquitination is a major mechanism of eukaryotic posttranslational protein turnover that has been implicated in abscisic acid (ABA)-mediated drought stress response. Here, we isolated T-DNA insertion mutant lines in which ABA-insensitive RING protein 5 (AtAIRP5) was suppressed, resulting in hyposensitive ABA-mediated germination compared to wild-type Arabidopsis (Arabidopsis thaliana) plants. A homology search revealed that AtAIRP5 is identical to gibberellin (GA) receptor RING E3 ubiquitin (Ub) ligase (GARU), which downregulates GA signaling by degrading the GA receptor GID1, and thus AtAIRP5 was renamed AtAIRP5/GARU. The atairp5/garu knockout progeny were impaired in ABA-dependent stomatal closure and were markedly more susceptible to drought stress than wild-type plants, indicating a positive role for AtAIRP5/GARU in the ABA-mediated drought stress response. Yeast two-hybrid, pull-down, target ubiquitination, and in vitro and in planta degradation assays identified serine carboxypeptidase-like1 (AtSCPL1), which belongs to the clade 1A AtSCPL family, as a ubiquitinated target protein of AtAIRP5/GARU. atscpl1 single and atairp5/garu-1 atscpl1-2 double mutant plants were more tolerant to drought stress than wild-type plants in an ABA-dependent manner, suggesting that AtSCPL1 is genetically downstream of AtAIRP5/GARU. After drought treatment, the endogenous ABA levels in atscpl1 and atairp5/garu-1 atscpl1-2 mutant leaves were higher than those in wild-type and atairp5/garu leaves. Overall, our results suggest that AtAIRP5/GARU RING E3 Ub ligase functions as a positive regulator of the ABA-mediated drought response by promoting the degradation of AtSCPL1.

Crop Root Responses to Drought Stress: Molecular Mechanisms, Nutrient Regulations, and Interactions with Microorganisms in the Rhizosphere

Roots play important roles in determining crop development under drought. Under such conditions, the molecular mechanisms underlying key responses and interactions with the rhizosphere in crop roots remain limited compared with model species such as Arabidopsis. This article reviews the molecular mechanisms of the morphological, physiological, and metabolic responses to drought stress in typical crop roots, along with the regulation of soil nutrients and microorganisms to these responses. Firstly, we summarize how root growth and architecture are regulated by essential genes and metabolic processes under water-deficit conditions. Secondly, the functions of the fundamental plant hormone, abscisic acid, on regulating crop root growth under drought are highlighted. Moreover, we discuss how the responses of crop roots to altered water status are impacted by nutrients, and vice versa. Finally, this article explores current knowledge of the feedback between plant and soil microbial responses to drought and the manipulation of rhizosphere microbes for improving the resilience of crop production to water stress. Through these insights, we conclude that to gain a more comprehensive understanding of drought adaption mechanisms in crop roots, future studies should have a network view, linking key responses of roots with environmental factors.

Melatonin Mediates Axillary Bud Outgrowth by Improving Nitrogen Assimilation and Transport in Rice

Melatonin plays an important role in plant resistance to biotic and abiotic stresses. However, whether melatonin is involved in the regulation of plant architecture, such as the formation of axillary bud outgrowth or tillering, in rice remains unknown. Here, we found that different concentrations of melatonin influenced axillary bud outgrowth in rice, and moderate melatonin concentrations also alleviated the inhibition of axillary bud outgrowth in the presence of high concentrations of basic amino acids lysine and arginine. Furthermore, transcriptome analysis demonstrated that genes involved in nitrogen metabolism and phytohormone signal transduction pathways may affect axillary bud outgrowth, which is regulated by melatonin. We determined that the differentially expressed genes glutamine synthetase OsGS2 and amino acid transporter OsAAP14, which are involved in nitrogen metabolism and are regulated by melatonin and basic amino acids, were the key regulators of axillary bud outgrowth in rice. In addition, we validated the functions of OsGS2 and OsAAP14 using rice transgenic plants with altered axillary bud outgrowth and tillers. Taken together, these results suggest that melatonin mediates axillary bud outgrowth by improving nitrogen assimilation and transport in rice.

BSA-Seq and Fine Linkage Mapping for the Identification of a Novel Locus (qPH9) for Mature Plant Height in Rice (Oryza sativa)

BACKGROUND

Plant height is a key factor in the determination of rice yield since excessive height can easily cause lodging and reduce yield. Therefore, the identification and analysis of plant height-related genes to elucidate their physiological, biochemical, and molecular mechanisms have significant implications for rice breeding and production.

RESULTS

High-throughput quantitative trait locus (QTL) sequencing analysis of a 638-individual F2:3 mapping population resulted in the identification of a novel height-related QTL (qPH9), which was mapped to a 2.02-Mb region of Chromosome 9. Local QTL mapping, which was conducted using 13 single nucleotide polymorphism (SNP)-based Kompetitive allele-specific PCR (KASP) markers for the qPH9 region, and traditional linkage analysis, facilitated the localization of qPH9 to a 126-kb region that contained 15 genes. Subsequent haplotype and sequence analyses indicated that OsPH9 was the most probable candidate gene for plant height at this locus, and functional analysis of osph9 CRISPR/Cas9-generated OsPH9 knockout mutants supported this conclusion.

CONCLUSION

OsPH9 was identified as a novel regulatory gene associated with plant height in rice, along with a height-reducing allele in 'Dongfu-114' rice, thereby representing an important molecular target for rice improvement. The findings of the present study are expected to spur the investigation of genetic mechanisms underlying rice plant height and further the improvement of rice plant height through marker-assisted selection.

ipa1 improves rice drought tolerance at seedling stage mainly through activating abscisic acid pathway

KEY MESSAGE: ipa1 enhances rice drought tolerance mainly through activating the ABA pathway. It endows rice seedlings with a more developed root system, smaller leaf stomata aperture, and enhanced carbon metabolism. Drought is a major abiotic stress to crop production. IPA1 (IDEAL PLANT ARCHITECTURE 1)/OsSPL14 encodes a transcription factor and has been reported to function in both rice ideal plant architecture and biotic resistance. Here, with a pair of IPA1 and ipa1-NILs (Near Iso-genic Lines), we found that ipa1 could significantly improve rice drought tolerance at seedling stage. The ipa1 plants had a better-developed root system and smaller leaf stomatal aperture. Analysis of carbon-nitrogen metabolism-associated enzyme activity, gene expression, and metabolic profile indicated that ipa1 could tip the carbon-nitrogen metabolism balance towards an increased carbon metabolism pattern. In both the control and PEG-treated conditions, ABA content in the ipa1 seedlings was significantly higher than that in the IPA1 seedlings. Expression of the ABA biosynthesis genes was detected to be up-regulated, whereas the expression of ABA catabolism genes was down-regulated in the ipa1 seedlings. In addition, based on yeast one-hybrid assay and dual-luciferase assay, IPA1 was found to directly activate the promoter activity of OsHOX12, a transcription factor promoting ABA biosynthesis, and OsNAC52, a positive regulator of the ABA pathway. The expression of OsHOX12 and OsNAC52 was significantly up-regulated in the ipa1 plants. Combined with the previous studies, our results suggested that ipa1 could improve rice seedling drought tolerance mainly through activating the ABA pathway and that regulation of the ipa1-mediated ABA pathway will be an important strategy for improving drought resistance of rice.

A novel insight into transcriptional and epigenetic regulation underlying sex expression and flower development in melon (Cucumis melo L.)

Melon (Cucumis melo L.) is an important cucurbit and has been considered as a model plant for studying sex determination. The four most common sexual morphotypes in melon are monoecious (A-G-M), gynoecious (--ggM-), andromonoecious (A-G-mm), and hermaphrodite (--ggmm). Sex expression in melons is complex, as the genes and associated networks that govern the sex expression are not fully explored. Recently, RNA-seq transcriptomic profiling, ChIP-qPCR analysis integrated with gene ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathways predicted the differentially expressed genes including sex-specific ACS and ACO genes, in regulating the sex-expression, phytohormonal cross-talk, signal transduction, and secondary metabolism in melons. Integration of transcriptional control through genetic interaction in between the ACS7, ACS11, and WIP1 in epistatic or hypostatic manner, along with the recruitment of H3K9ac and H3K27me3, epigenetically, overall determine sex expression. Alignment of protein sequences for establishing phylogenetic evolution, motif comparison, and protein-protein interaction supported the structural conservation while presence of the conserved hydrophilic and charged residues across the diverged evolutionary group predicted the functional conservation of the ACS protein. Presence of the putative cis-binding elements or DNA motifs, and its further comparison with DAP-seq-based cistrome and epicistrome of Arabidopsis, unraveled strong ancestry of melons with Arabidopsis. Motif comparison analysis also characterized putative genes and transcription factors involved in ethylene biosynthesis, signal transduction, and hormonal cross-talk related to sex expression. Overall, we have comprehensively reviewed research findings for a deeper insight into transcriptional and epigenetic regulation of sex expression and flower development in melons.

The molecular and genetic regulation of shoot branching

The architecture of flowering plants exhibits both phenotypic diversity and plasticity, determined, in part, by the number and activity of axillary meristems and, in part, by the growth characteristics of the branches that develop from the axillary buds. The plasticity of shoot branching results from a combination of various intrinsic and genetic elements, such as number and position of nodes and type of growth phase, as well as environmental signals such as nutrient availability, light characteristics, and temperature (Napoli et al., 1998; Bennett and Leyser, 2006; Janssen et al., 2014; Teichmann and Muhr, 2015; Ueda and Yanagisawa, 2019). Axillary meristem initiation and axillary bud outgrowth are controlled by a complex and interconnected regulatory network. Although many of the genes and hormones that modulate branching patterns have been discovered and characterized through genetic and biochemical studies, there are still many gaps in our understanding of the control mechanisms at play. In this review, we will summarize our current knowledge of the control of axillary meristem initiation and outgrowth into a branch.

Identification and Characterization of Short Crown Root 8, a Temperature-Sensitive Mutant Associated with Crown Root Development in Rice

Crown roots are essential for plants to obtain water and nutrients, perceive environmental changes, and synthesize plant hormones. In this study, we identified and characterized short crown root 8 (scr8), which exhibited a defective phenotype of crown root and vegetative development. Temperature treatment showed that scr8 was sensitive to temperature and that the mutant phenotypes were rescued when grown under low temperature condition (20 °C). Histological and EdU staining analysis showed that the crown root formation was hampered and that the root meristem activity was decreased in scr8. With map-based cloning strategy, the SCR8 gene was fine-mapped to an interval of 126.4 kb on chromosome 8. Sequencing analysis revealed that the sequence variations were only found in LOC_Os08g14850, which encodes a CC-NBS-LRR protein. Expression and inoculation test analysis showed that the expression level of LOC_Os08g14850 was significantly decreased under low temperature (20 °C) and that the resistance to Xanthomonas oryzae pv. Oryzae (Xoo) was enhanced in scr8. These results indicated that LOC_Os08g14850 may be the candidate of SCR8 and that its mutation activated the plant defense response, resulting in a crown root growth defect.

Genome editing in cereal crops: an overview

Genome-editing technologies offer unprecedented opportunities for crop improvement with superior precision and speed. This review presents an analysis of the current state of genome editing in the major cereal crops- rice, maize, wheat and barley. Genome editing has been used to achieve important agronomic and quality traits in cereals. These include adaptive traits to mitigate the effects of climate change, tolerance to biotic stresses, higher yields, more optimal plant architecture, improved grain quality and nutritional content, and safer products. Not all traits can be achieved through genome editing, and several technical and regulatory challenges need to be overcome for the technology to realize its full potential. Genome editing, however, has already revolutionized cereal crop improvement and is poised to shape future agricultural practices in conjunction with other breeding innovations.

Modification of cereal plant architecture by genome editing to improve yields

KEY MESSAGE

We summarize recent genome editing studies that have focused on the examination (or reexamination) of plant architectural phenotypes in cereals and the modification of these traits for crop improvement. Plant architecture is defined as the three-dimensional organization of the entire plant. Shoot architecture refers to the structure and organization of the aboveground components of a plant, reflecting the developmental patterning of stems, branches, leaves and inflorescences/flowers. Root system architecture is essentially determined by four major shape parameters-growth, branching, surface area and angle. Interest in plant architecture has arisen from the profound impact of many architectural traits on agronomic performance, and the genetic and hormonal regulation of these traits which makes them sensitive to both selective breeding and agronomic practices. This is particularly important in staple crops, and a large body of literature has, therefore, accumulated on the control of architectural phenotypes in cereals, particularly rice due to its twin role as one of the world's most important food crops as well as a model organism in plant biology and biotechnology. These studies have revealed many of the molecular mechanisms involved in the regulation of tiller/axillary branching, stem height, leaf and flower development, root architecture and the grain characteristics that ultimately help to determine yield. The advent of genome editing has made it possible, for the first time, to introduce precise mutations into cereal crops to optimize their architecture and close in on the concept of the ideotype. In this review, we consider recent genome editing studies that have focused on the examination (or reexamination) of plant architectural phenotypes in cereals and the modification of these traits for crop improvement.

The Role of Anaphase-Promoting Complex/Cyclosome (APC/C) in Plant Reproduction

Most eukaryotic species propagate through sexual reproduction that requires male and female gametes. In flowering plants, it starts through a single round of DNA replication (S phase) and two consecutive chromosome segregation (meiosis I and II). Subsequently, haploid mitotic divisions occur, which results in a male gametophyte (pollen grain) and a female gametophyte (embryo sac) formation. In order to obtain viable gametophytes, accurate chromosome segregation is crucial to ensure ploidy stability. A precise gametogenesis progression is tightly regulated in plants and is controlled by multiple mechanisms to guarantee a correct evolution through meiotic cell division and sexual differentiation. In the past years, research in the field has shown an important role of the conserved E3-ubiquitin ligase complex, Anaphase-Promoting Complex/Cyclosome (APC/C), in this process. The APC/C is a multi-subunit complex that targets proteins for degradation via proteasome 26S. The functional characterization of APC/C subunits in Arabidopsis, which is one of the main E3 ubiquitin ligase that controls cell cycle, has revealed that all subunits investigated so far are essential for gametophytic development and/or embryogenesis.

The Cyclin CYCA3;4 Is a Postprophase Target of the APC/CCCS52A2 E3-Ligase Controlling Formative Cell Divisions in Arabidopsis

The anaphase promoting complex/cyclosome (APC/C) controls unidirectional progression through the cell cycle by marking key cell cycle proteins for proteasomal turnover. Its activity is temporally regulated by the docking of different activating subunits, known in plants as CELL DIVISION PROTEIN20 (CDC20) and CELL CYCLE SWITCH52 (CCS52). Despite the importance of the APC/C during cell proliferation, the number of identified targets in the plant cell cycle is limited. Here, we used the growth and meristem phenotypes of Arabidopsis (Arabidopsis thaliana) CCS52A2-deficient plants in a suppressor mutagenesis screen to identify APC/CCCS52A2 substrates or regulators, resulting in the identification of a mutant cyclin CYCA3;4 allele. CYCA3;4 deficiency partially rescues the ccs52a2-1 phenotypes, whereas increased CYCA3;4 levels enhance the scored ccs52a2-1 phenotypes. Furthermore, whereas the CYCA3;4 protein is promptly broken down after prophase in wild-type plants, it remains present in later stages of mitosis in ccs52a2-1 mutant plants, marking it as a putative APC/CCCS52A2 substrate. Strikingly, increased CYCA3;4 levels result in aberrant root meristem and stomatal divisions, mimicking phenotypes of plants with reduced RETINOBLASTOMA-RELATED PROTEIN1 (RBR1) activity. Correspondingly, RBR1 hyperphosphorylation was observed in CYCA3;4 gain-of-function plants. Our data thus demonstrate that an inability to timely destroy CYCA3;4 contributes to disorganized formative divisions, possibly in part caused by the inactivation of RBR1.