No abstract

Preharvest sprouting (PHS) is an unfavorable trait in cereal crops and causes serious yield loss. However, the molecular mechanism underlying PHS remains largely elusive. Here, we identified a member of 9-cis-epoxycarotenoid dioxygenase family, OsNCED3, which regulates PHS and grain development in rice (Oryza sativa L.).OsNCED3 encodes a chloroplast-localized abscisic acid (ABA) biosynthetic enzyme highly expressed in the embryo of developing seeds. Disruption of OsNCED3 by CRISPR/Cas9-mediated mutagenesis led to a lower ABA and higher gibberellic acid (GA) levels (thus a skewed ABA/GA ratio) in the embryo, promoting embryos growth and breaking seed dormancy before seed maturity and harvest, thus decreased seed dormancy and enhanced PHS in rice. However, the overexpression of OsNCED3 enhanced PHS resistance by regulating proper ABA/GA ratio in the embryo. Intriguingly, the overexpression of OsNCED3 resulted in increased grain size and weight, whereas the disruption of OsNCED3 function decreased grain size and weight. Nucleotide diversity analyses suggested that OsNCED3 may be selected during japonica populations adaptation of seed dormancy and germination. Taken together, we have identified a new OsNCED regulator involved rice PHS and grain development, and provide a potential target gene for improving PHS resistance and grain development in rice.

Chilling stress has become a major limiting factor that reduces crop productivity worldwide. In this study, we identified a new gene bHLH57, whose product enhances chilling tolerance in rice at diverse developmental stages. bHLH57 was mainly expressed in leaves and anthers, and its protein was targeted to the nucleus. Overexpression of bHLH57 enhanced chilling tolerance by increasing trehalose synthesis, whereas its mutants by CRISPR/Cas9‐mediated mutagenesis were more sensitive to chilling and had reduced trehalose. Meanwhile, bHLH57 may regulate ROS metabolism and CBFs/DREBs‐ dependent pathways in response to chilling stress. In addition, the overexpression of bHLH57 resulted in increased grain yield under normal and chilling conditions, however, the disruption of bHLH57 displayed decreased grain size and seed setting rate, thus reduced grain yield. Phylogenetic and nucleotide diversity analyses suggested that bHLH57 is relatively conserved in monocotyledons, and may be selected during indica populations adaptation. Taken together, we have identified a new bHLH regulator involved rice chilling tolerance and grain yield, and provide a potential target gene for improving chilling tolerance and grain yield of rice.

Genetic transformation is an important strategy for revealing gene function, and it is used extensively in both functional genomics study and molecular breeding of rice. Demand for its application in wild Oryza species is rising for their extensive genetic diversity. However, genetic transformation of wild Oryza accessions with AA genome using calli induced from scutellum tissue of embryos in mature seeds has not been successfully established. In the present study, we used Chaling common wild rice (CLCWR) (Oryza rufipogon Griff.) with AA genome to successfully establish an Agrobacterium-mediated genetic transformation system based on scutellum tissue of embryos in mature seeds. The calli from embryos in mature seeds of CLCWR were easy to be induced and regenerated. The callus induction rate and texture were optimum under 2.5 mg/L 2,4-D. The optimal hormone combination used for regeneration was 2 mg/L ZT + 0.1 mg/L NAA. Studies on genetic transformation and genome editing showed that the transformation efficiency was 87–94%, the efficiency of single genome editing and multiplex genome editing were about 60–70% and 20–40%, respectively. Compared with Nipponbare (Nip), CLCWR had higher Hygromycin-resistant callus frequency and transformation efficiency. Taken together, our study establishes a highly efficient transformation system for common wild rice with AA genome and provides a good rice material for de novo domestication by genome editing in the future.

Zhu1S is a thermosensitive genic male-sterile (TGMS) line of rice possessing outstanding combining ability and low critical temperature, which has been extensively utilized as a female parent in two-line hybrid ricebreeding. However, the fertility of Zhu 1S during hybrid seed production is frequently affected by high temperature, thus leading to its fertility alteration and aborted hybrid seed production. To understand its fertility conversion mechanism under high temperature, we employed transcriptomics analyses on the anthers of young panicles of Zhu 1S during the fertility alternation sensitivity stage under high (Zhu 1S-H) and low (Zhu 1S-L) temperatures. The results showed that a total of 1119 differentially expressed genes (DEGs) were identified between Zhu 1S-H and Zhu1S-L anthers, including 680 up-regulated and 439 down-regulated genes. Bioinformatics analysis of these DEGs revealed that the high temperature induction caused fertility-sterility conversion in Zhu1S, mainly by decreasing the mRNA abundances of important genes closely related to plant hormone and MAPK signal pathway and transcriptional regulation factors, thereby impeding the growth and development of the anther of Zhu 1S, which ultimately affected the fertility transition of Zhu 1S under high temperature. The protein–protein interaction network analysis indicates that transcription factor OsTIFY11C possibility plays a central role in the fertility transition of Zhu 1S under high temperature.The present studies offer a theoretical foundation for further research into the molecular mechanism underlying fertility conversion in TGMS line Zhu 1S.