OsSIZ2 regulates nitrogen homeostasis and some of the reproductive traits in rice

Genetic variation in ZmKW1 contributes to kernel weight and size in dent corn and popcorn

Kernel weight is a critical factor that essentially affects maize (Zea mays) yield. In natural inbred lines, popcorn kernels exhibit overtly smaller sizes compared to dent corn kernels, and kernel weight, which is controlled by multiple genetic loci, varies widely. Here, we characterized a major quantitative trait locus on chromosome 1, responsible for controlling kernel weight (qKW1) and size. The qKW1 locus encodes a protein containing a seven in absentia domain with E3 ubiquitin ligase activity, expressed prominently from the top to the middle region of the endosperm. The presence and function of qKW1 were confirmed through ZmKW1 gene editing, where the mutations in ZmKW1 within dent corn significantly increased kernel weight, consistent with alterations in kernel size, while overexpression of ZmKW1 had the opposite effect. ZmKW1 acts as a negative regulator of kernel weight and size by reducing both the number and size of the endosperm cells and impacting endosperm filling. Notably, the popcorn allele qKW1N and the dent corn allele qKW1D encode identical proteins; however, the differences in promoter activity arise due to the insertion of an Indel-1346 sequence in the qKW1N promoter, resulting in higher expression levels compared to qKW1D, thus contributing to the variation in kernel weight and size between popcorn and dent corn kernels. Linkage disequilibrium analysis of the 2.8 kb promoter region of ZmKW1 in a dataset comprising 111 maize association panels identified two distinct haplotypes. Our results provide insight into the mechanisms underlying kernel development and yield regulation in dent corn and popcorn, with a specific focus on the role of the ubiquitination system.

Cytological Observation and RNA-Seq Analyses Reveal miR9564 and Its Target Associated with Pollen Sterility in Autotetraploid Rice

Understanding the regulation of autotetraploid sterility is essential for harnessing the strong advantages in genomic buffer capacity, biodiversity, and heterosis of autotetraploid rice. miRNAs play crucial roles in fertility regulation, yet information about their reproductive roles and target genes in tetraploid rice remains limited. Here, we used three tetraploid lines, H1 (fertile), HF (fertile), and LF (sterile), to investigate cytological features and identify factors associated with autotetraploid sterility. LF showed abnormal meiosis, resulting in low pollen fertility and viability, ultimately leading to scarce fertilization and a low-seed setting compared to H1 and HF. RNA-seq revealed 30 miRNA-candidate target pairs related to autotetraploid pollen sterility. These pairs showed opposite expression patterns, with differential expression between fertile lines (H1 and HF) and the sterile line (LF). qRT-PCR confirmed that miR9564, miR528, and miR27874 were highly expressed in the anthers of H1 and HF but not in LF, while opposite results were obtained in their targets (ARPS, M2T, and OsRPC53). Haplotype and expression pattern analyses revealed that ARPS was specifically expressed in lines with the same haplotype of MIR9564 (the precursor of miR9564) as LF. Furthermore, the Dual-GFP assay verified that miR9564 inhibited the fluorescence signal of ARPS-GFP. The over-expression of ARPS significantly decreased the seed setting rate (59.10%) and pollen fertility (50.44%) of neo-tetraploid rice, suggesting that ARPS plays important roles in autotetraploid pollen sterility. This study provides insights into the cytological characteristic and miRNA expression profiles of tetraploid lines with different fertility, shedding light on the role of miRNAs in polyploid rice.

Small ubiquitin-like modifiers E3 ligases in plant stress

Plants regularly encounter various environmental stresses such as salt, drought, cold, heat, heavy metals and pathogens, leading to changes in their proteome. Of these, a post-translational modification, SUMOylation is particularly significant for its extensive involvement in regulating various plant molecular processes to counteract these external stressors. Small ubiquitin-like modifiers (SUMO) protein modification significantly contributes to various plant functions, encompassing growth, development and response to environmental stresses. The SUMO system has a limited number of ligases even in fully sequenced plant genomes but SUMO E3 ligases are pivotal in recognising substrates during the process of SUMOylation. E3 ligases play pivotal roles in numerous biological and developmental processes in plants, including DNA repair, photomorphogenesis, phytohormone signalling and responses to abiotic and biotic stress. A considerable number of targets for E3 ligases are proteins implicated in reactions to abiotic and biotic stressors. This review sheds light on how plants respond to environmental stresses by focusing on recent findings on the role of SUMO E3 ligases, contributing to a better understanding of how plants react at a molecular level to such stressors.

Weighted gene co-expression network analysis of nitrogen (N)-responsive genes and the putative role of G-quadruplexes in N use efficiency (NUE) in rice

Rice is an important target to improve crop nitrogen (N) use efficiency (NUE), and the identification and shortlisting of the candidate genes are still in progress. We analyzed data from 16 published N-responsive transcriptomes/microarrays to identify, eight datasets that contained the maximum number of 3020 common genes, referred to as N-responsive genes. These include different classes of transcription factors, transporters, miRNA targets, kinases and events of post-translational modifications. A Weighted gene co-expression network analysis (WGCNA) with all the 3020 N-responsive genes revealed 15 co-expression modules and their annotated biological roles. Protein-protein interaction network analysis of the main module revealed the hub genes and their functional annotation revealed their involvement in the ubiquitin process. Further, the occurrences of G-quadruplex sequences were examined, which are known to play important roles in epigenetic regulation but are hitherto unknown in N-response/NUE. Out of the 3020 N-responsive genes studied, 2298 contained G-quadruplex sequences. We compared these N-responsive genes containing G-quadruplex sequences with the 3601 genes we previously identified as NUE-related (for being both N-responsive and yield-associated). This analysis revealed 389 (17%) NUE-related genes containing G-quadruplex sequences. These genes may be involved in the epigenetic regulation of NUE, while the rest of the 83% (1811) genes may regulate NUE through genetic mechanisms and/or other epigenetic means besides G-quadruplexes. A few potentially important genes/processes identified as associated with NUE were experimentally validated in a pair of rice genotypes contrasting for NUE. The results from the WGCNA and G4 sequence analysis of N-responsive genes helped identify and shortlist six genes as candidates to improve NUE. Further, the hitherto unavailable segregation of genetic and epigenetic gene targets could aid in informed interventions through genetic and epigenetic means of crop improvement.

A SUMO ligase OsMMS21 regulates rice development and auxin response

SUMOylation, which transfers the Small Ubiquitin-related Modifier (SUMO) polypeptides to target proteins, regulates diverse cellular processes in eukaryotes. The SUMO conjugation reaction is usually promoted by SUMO E3 ligases, but the molecular functions of this type of enzymes remain unclear in cereal crops. Here, OsMMS21, a SUMO E3 ligase, was functionally characterized in rice (Oryza sativa). Bioinformatics analysis showed that OsMMS21 harbors a conserved SP-RING domain that is essential for the activity of SUMO ligases. Biochemical data indicated that this protein is auto-SUMOylated. Besides, overexpression of OsMMS21 rescued the developmental defects of the AtMMS21 mutant, supporting that OsMMS21 is a functional homolog of the Arabidopsis SUMO ligase AtMMS21. The OsMMS21 rice T-DNA mutant displays a short-root and dwarfism phenotype. RNA-seq data revealed that the expression levels of many genes involved in signaling transduction of hormones, including auxin, are altered in the OsMMS21 mutant. Further results under the auxin treatment showed that the OsMMS21 mutant is insensitive to auxin. Collectively, our results demonstrated the molecular features of OsMMS21 and uncovered the roles of this SUMO ligase in development and auxin response, providing hints for further studies on protein SUMOylation in rice.

Knockdown of OsSAE1a affects the growth and development and phosphate homeostasis in rice

SUMOylation is a post-translational modification process that comprises a tandem enzymatic cascade, i.e., maturation, activation, conjugation, and ligation of a small ubiquitin-like modifier, which triggers the modulated activities and transport of the cellular proteins to other areas of the cell. In Oryza sativa (rice), OsSIZ1/2 encoding E3 SUMO ligase exerts regulatory influences on Pi homeostasis and developmental responses. However, the role of OsSAE1a, SUMO E1 activating enzyme, in regulating phosphate (Pi) utilization and/or growth and development is not known in rice and was thus investigated in this study. The qRT-PCR assay revealed a constitutive and variable spatiotemporal expression pattern of OsSAE1a in the vegetative and reproductive tissues and was comparable in the root and shoot grown under different Pi regimes. RNAi-mediated suppression of OsSAE1a exerted variable effects on the concentrations of Pi and total P in different tissues, uptake and distribution of ³²Pi, and relative expression levels of several genes that play pivotal roles in the maintenance of Pi homeostasis. The effects of the mutation in OsSAE1a were also evident in the vegetative and reproductive traits of rice during growth in a hydroponic system and pot soil, respectively. Overall, these results suggest a broad-spectrum role of OsSAE1a in the maintenance of Pi homeostasis and regulating growth and development.

Identification of fertility-related genes for maize CMS-S via Bulked Segregant RNA-Seq

Cytoplasmic male sterility (CMS) is extensively used in maize hybrid production, and identification of genes related to fertility restoration for CMS is important for hybrid breeding. The fertility restoration of S type CMS is governed by several loci with major and minor effects, while the mechanism of fertility restoration for CMS-S is still unknown. In this study, BSR-Seq was conducted with two backcrossing populations with the fertility restoration genes, Rf3 and Rf10, respectively. Genetic mapping via BSR-Seq verified the positions of the two loci. A total of 353 and 176 differentially expressed genes (DEGs) between the male fertility and male sterile pools were identified in the populations with Rf3 and Rf10, respectively. In total, 265 DEGs were co-expressed in the two populations, which were up-regulated in the fertile plants, and they might be related to male fertility involving in anther or pollen development. Moreover, 35 and seven DEGs were specifically up-regulated in the fertile plants of the population with Rf3 and Rf10, respectively. Function analysis of these DEGs revealed that jasmonic acid (JA) signal pathway might be involved in the Rf3 mediated fertility restoration for CMS-S, while the small ubiquitin-related modifier system could play a role in the fertility restoration of Rf10.

Exploring the regulatory levels of SUMOylation to increase crop productivity

SUMOylation is an essential post-translational modification that affects several cellular processes, from gene replication to stress response. Studies using the SUMO (de)conjugation machinery have provided evidence regarding its potential to improve crop performance and productivity under normal and adverse conditions. However, the pleiotropic effect of SUMOylation can be a disadvantage in both situations, especially when considering unpredictable environmental conditions caused by climate changes. Here, we discuss the pleiotropic effects caused by disrupting the SUMOylation machinery, and new strategies that may help to overcome pleiotropy. We propose exploring the several regulatory levels of SUMOylation recently revealed, including transcriptional, post-transcriptional regulation by alternative splicing, and post-translational modifications. These new findings may provide valuable tools to increase crop productivity.