Significance: Premature leaf senescence is known to decrease rice yield severely, but the molecular mechanism underlying this relationship remains largely unknown. Similarly, although abscisic acid (ABA)-induced leaf senescence has long been observed, the mechanism of this pathway has yet to be determined. In this study we identified and characterized a dominant premature leaf senescence mutant, prematurely senile 1 ( ps1-D ). The data demonstrated both that PS1/Oryza sativa NAC (no apical meristem, Arabidopsis ATAF1/2, and cup-shaped cotyledon2)-like, activated by apetala3/pistillata ( OsNAP ) is an ideal marker of natural senescence onset and that it functions as an important link between ABA and leaf senescence in rice. Furthermore, reduced OsNAP expression led to extended grain filling and an improved seed-setting rate, which significantly enhanced the grain yield. Thus, fine-tuning OsNAP expression should be a means of improving rice yield.

Japonica/geng and indica/xian are two major rice (Oryza sativa) subspecies with multiple divergent traits, but how these traits are related and interact within each subspecies remains elusive. Brassinosteroids (BRs) are a class of steroid phytohormones that modulate many important agronomic traits in rice. Here, using different physiological assays, we revealed that japonica rice exhibits an overall lower BR sensitivity than indica. Extensive screening of BR signaling genes led to the identification of a set of genes distributed throughout the primary BR signaling pathway with divergent polymorphisms. Among these, we demonstrate that the C38/T variant in BR Signaling Kinase2 (OsBSK2), causing the amino acid change P13L, plays a central role in mediating differential BR signaling in japonica and indica rice. OsBSK2^L13 in indica plays a greater role in BR signaling than OsBSK2^P13 in japonica by affecting the auto‐binding and protein accumulation of OsBSK2. Finally, we determined that OsBSK2 is involved in a number of divergent traits in japonica relative to indica rice, including grain shape, tiller number, cold adaptation, and nitrogen‐use efficiency. Our study suggests that the natural variation in OsBSK2 plays a key role in the divergence of BR signaling, which underlies multiple divergent traits between japonica and indica.

Amylose content (AC) and viscosity profile are primary indices for evaluating eating and cooking qualities of rice grain. Using chromosome segment substitution lines (CSSLs), previous studies identified a QTL cluster of genes for rice eating and cooking quality in the interval R727–G1149 on chromosome 8. In this study we report two QTLs for viscosity parameters, respectively controlling setback viscosity (SBV) and consistency viscosity (CSV), located in the same interval using rapid viscosity analyzer (RVA) profile as an indicator of eating quality. Previously reported QTL for AC was dissected into two components with opposite genetic effects. Of four QTLs, qCSV-8 and qAC-8-2 had stable genetic effects across three and four environments, respectively. qSBV-8, qCSV-8 and qAC-8-1 partly overlapped, but were separated from qAC-8-2. Based on data from an Affymetrix rice GeneChip, two genes related to starch biosynthesis at the qAC-8-2 locus were chosen for further quantitative expression analysis. Both genes showed enhanced expression in sub-CSSLs carrying the target qAC-8-2 allele, but not in sub-CSSLs without the target qAC-8-2 allele, indicating their possible role in rice quality determination. Molecular markers closely linked to the two stable QTL provide the opportunity for marker-assisted selection (MAS) in breeding high quality rice.

Direct seeding of rice (Oryza sativa L.) is a low-labor and sustainable cultivation method that is used worldwide. Seed vigor and early vigor are important traits associated with seedling stand density (SSD) and weed competitive ability (WCA), which are key factors in direct-seeded rice (DSR) cultivation systems. Here, we developed a set of chromosome segment substitution lines with Xiushui134 as receptor parent and Yangdao6 as donor parent and used these lines as a mapping population to identify quantitative trait loci (QTLs) for seed vigor, which we evaluated based on germinability–related indicators (germination percentage (GP), germination energy (GE), and germination index (GI)) and seedling vigor–related indicators (root number (RN), root length (RL), and shoot length (SL) at 14 days after imbibition) under controlled conditions in an incubator. Ten QTLs were detected across four chromosomes, of which a cluster of QTLs (qGP11, qGE11, qGI11, and qRL11) co-localized on Chr. 11 with high LOD values (12.03, 8.13, 7.14, and 8.75, respectively). Fine mapping narrowed down the QTL cluster to a 0.7-Mb interval between RM26797 and RM6680. Further analysis showed that the QTL cluster has a significant effect (p < 0.01) on early vigor under hydroponic culture (root length, total dry weight) and direct seeding conditions (tiller number, aboveground dry weight). Thus, our combined analysis revealed that the QTL cluster influenced both seed vigor and early vigor. Identifying favorable alleles at this QTL cluster could facilitate the improvement of SSD and WCA, thereby addressing both major factors in DSR cultivation systems.

Background: CCCH zinc finger proteins (OsC3Hs) are a class of transcriptional regulators that play important roles in plant development and stress responses. Although their functional significance has been widely studied in model species, comprehensive genome-wide characterization of CCCH proteins in rice (Oryza sativa) remains limited. Methods: Using Arabidopsis CCCH proteins as references, we identified the CCCH gene family in rice and analyzed the physicochemical properties, subcellular localization, conserved structures, phylogeny, cis-regulatory elements, synteny analysis, spatiotemporal expression patterns, and expression patterns under drought, ABA, and MeJA treatments for the identified CCCH family members. Results: The results showed that the rice CCCH family comprises 73 members, which are unevenly distributed across the 12 chromosomes. Phylogenetic analysis classified them into 11 subfamilies. Subcellular localization indicated that most members are localized in the nucleus. The upstream regions of CCCH promoters contain a large number of cis-regulatory elements related to plant hormones and biotic stress responses. Most genes respond to drought, abscisic acid (ABA), and methyl jasmonate (MeJA) treatments. OsC3H36 was highly expressed under drought, ABA, and MeJA treatments. Haplotype analysis of this gene revealed two major allelic variants (H1 and H2), with H1 predominantly found in japonica rice and associated with increased grain width and 1000-grain weight. Functional validation using a chromosome segment substitution line (CSSL1) confirmed these findings. Conclusions: CCCH genes play important roles in rice growth, development, and stress responses. Additionally, we validated that OsC3H36 is associated with rice grain width and 1000-grain weight.