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Soil salinization limits rice growth and is an important restriction on grain yield. Jacalin-related lectins are involved in multiple stress responses, but their role in salt stress responses and use as molecular markers for salt tolerance remain poorly understood. Salt stress treatments and RT-qPCR analyses of Sea Rice 86 (SR86), 9311, and Nipponbare (Nip) showed that OsJRL45 and OsJRL40 enhanced tolerance of salt stress in SR86. Molecular markers based on sequence differences in SR86 and the salt-sensitive variety, 9311, in the intergenic region between OsJRL45 and OsJRL40 were validated in recombinant inbred lines derived from SR86 and 9311, hybrid populations, and common rice varieties. Yeast two-hybrid and bimolecular fluorescence complementation demonstrated that OsJRL45 and OsJRL40 interacted. Co-transformation of Nip with OsJRL45 and OsJRL40 derived from SR86 had no effect on the mature phenotype in T2 plants; however, salt stress at the three-leaf stage led to significant increases in CAT, POD, SOD, and Pro contents, but reduced MDA content in transgenic plants. Transcriptomic analysis identified 834 differentially expressed genes in transgenic plants under salt stress. GO and KEGG enrichment analyses indicated that metabolic pathways related to antioxidant responses and osmotic balance were crucial for salt-stress tolerance. Thus, molecular markers based on nucleotide differences in OsJRL45 and OsJRL40 provide a novel method for identifying salt-tolerant rice varieties. [ABSTRACT FROM AUTHOR]

Summary: Chilling stress has seriously limited the global production and geographical distribution of rice. However, the molecular mechanisms associated with plant responses to chilling stress are less known. In this study, we revealed a member of β‐ketoacyl‐ACP synthase I family (KASI), OsKASI‐2 which confers chilling tolerance in rice. OsKASI‐2 encodes a chloroplast‐localized KASI enzyme mainly expressed in the leaves and anthers of rice and strongly induced by chilling stress. Disruption of OsKASI‐2 led to decreased KAS enzymatic activity and the levels of unsaturated fatty acids, which impairs degree of unsaturation of membrane lipids, thus increased sensitivity to chilling stress in rice. However, the overexpression of OsKASI‐2 significantly improved the chilling tolerance ability in rice. In addition, OsKASI‐2 may regulate ROS metabolism in response to chilling stress. Natural variation of OsKASI‐2 might result in difference in chilling tolerance between indica and japonica accessions, and Hap1 of OsKASI‐2 confers chilling tolerance in rice. Taken together, we suggest OsKASI‐2 is critical for regulating degree of unsaturation of membrane lipids and ROS accumulation for maintenance of membrane structural homeostasis under chilling stress, and provide a potential target gene for improving chilling tolerance of rice. [ABSTRACT FROM AUTHOR]

Background: Rice (Oryza sativa L.) is one of the most widely cultivated grain crops in the world that meets the caloric needs of more than half the world's population. Salt stress seriously affects rice production and threatens food security. Therefore, mining salt tolerance genes in salt-tolerant germplasm and elucidating their molecular mechanisms in rice are necessary for the breeding of salt tolerant cultivars. Results: In this study, a salt stress-responsive jacalin-related lectin (JRL) family gene, OsJRL45, was identified in the salt-tolerant rice variety 'sea rice 86' (SR86). OsJRL45 showed high expression level in leaves, and the corresponding protein mainly localized to the endoplasmic reticulum. The knockout mutant and overexpression lines of OsJRL45 revealed that OsJRL45 positively regulates the salt tolerance of rice plants at all growth stages. Compared with the wild type (WT), the OsJRL45 overexpression lines showed greater salt tolerance at the reproductive stage, and significantly higher seed setting rate and 1,000-grain weight. Moreover, OsJRL45 expression significantly improved the salt-resistant ability and yield of a salt-sensitive indica cultivar, L6-23. Furthermore, OsJRL45 enhanced the antioxidant capacity of rice plants and facilitated the maintenance of Na+-K+ homeostasis under salt stress conditions. Five proteins associated with OsJRL45 were screened by transcriptome and interaction network analysis, of which one, the transmembrane transporter Os10g0210500 affects the salt tolerance of rice by regulating ion transport-, salt stress-, and hormone-responsive proteins. Conclusions: The OsJRL45 gene isolated from SR86 positively regulated the salt tolerance of rice plants at all growth stages, and significantly increased the yield of salt-sensitive rice cultivar under NaCl treatment. OsJRL45 increased the activity of antioxidant enzyme of rice and regulated Na+/K+ dynamic equilibrium under salinity conditions. Our data suggest that OsJRL45 may improve the salt tolerance of rice by mediating the expression of ion transport-, salt stress response-, and hormone response-related genes. [ABSTRACT FROM AUTHOR]

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. Summary statement: bHLH57 enhances chilling tolerance through regulation of trehalose synthase, ROS metabolism, and CBFs/DREBs‐ dependent pathways. In addition, the overexpressing of bHLH57 potentially improves grain yield by increasing the seed setting rate and grain size. Taken together, we provide a potential target gene for improving chilling tolerance and grain yield of rice [ABSTRACT FROM AUTHOR]

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. Summary statement: 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 that overexpression of OsNCED3 enhanced PHS resistance by regulating proper abscisic acidgibberellic acid ratio in the embryo. In addition, the overexpression of OsNCED3 resulted in increased grain size and weight. This study provides a potential target gene for improving PHS resistance and grain development in rice. [ABSTRACT FROM AUTHOR]

Salt stress seriously affects plant growth and development and reduces the yield of rice. Therefore, the development of salt-tolerant high-yielding rice cultivars through quantitative trait locus (QTL) identification and bulked segregant analysis (BSA) is the main focus of molecular breeding projects. In this study, sea rice (SR86) showed greater salt tolerance than conventional rice. Under salt stress, the cell membrane and chlorophyll were more stable and the antioxidant enzyme activity was higher in SR86 than in conventional rice. Thirty extremely salt-tolerant plants and thirty extremely salt-sensitive plants were selected from the F2 progenies of SR86 × Nipponbare (Nip) and SR86 × 9311 crosses during the whole vegetative and reproductive growth period and mixed bulks were generated. Eleven salt tolerance related candidate genes were located using QTL-seq together with BSA. Real time quantitative PCR (RT-qPCR) analysis showed that LOC_Os04g03320.1 and BGIOSGA019540 were expressed at higher levels in the SR86 plants than in Nip and 9311 plants, suggesting that these genes are critical for the salt tolerance of SR86. The QTLs identified using this method could be effectively utilized in future salt tolerance breeding programs, providing important theoretical significance and application value for rice salt tolerance breeding. [ABSTRACT FROM AUTHOR]

The widespread application of 'two-line' hybrid rice, based on temperature- and photoperiod-sensitive genic male-sterile lines, plays an important role in ensuring global food security. Such lines are fertile in short-day/low-temperature conditions when used for self-breeding, and sterile in long-day/high-temperature conditions when used for hybrid seed production. However, fertility instability and low hybrid seed production of sterile lines are urgent problems. The aim of this study was to increase the stability of pollen sterility by studying the critical sterile-inducing temperature and stigma vitality of 97 newly selected male-sterile lines in China from 2017 to 2020. Sterility gene source analysis showed that 89.7% of the materials contained the tms5 sterile gene. After 6 days of treatment at 23.5°C during the reproductive period, 42 male-sterile lines were sterile. After 10 days of treatment at 23.5°C, the sterility of 12 sterile lines remained stable, indicating a high level of safety for hybrid seed production. After 10 days of low-temperature treatment at 19°C, the fertile pollen rate of 47 of the 97 sterile lines was >70%, indicating a high level of seed reproduction safety. Only six of these 47 male-sterile lines could maintain low fertility after 10 days of treatment at 23.5°C, indicating that they could be used safely for both hybrid seed production and sterile line reproduction. The results of delayed pollination showed that among the six lines, only Zhong 7S had high stigma vitality, and BYXA1S and H10S-2 had medium stigma vitality. Therefore, those three sterile lines have the potential for safe hybrid seed production and high-yield seed reproduction. Based on our research, we propose a new breeding standard of dual-purpose male-sterile lines to promote the development of two-line hybrid rice. 'Two-line' hybrid rice plays an important role in ensuring global food security. However, fertility instability and low hybrid seed production of sterile lines are urgent problems. In order to increase the stability of pollen sterility, we compared the low-temperature tolerance of fertile pollen development and outcrossing characteristics of new dual-purpose genic male-sterile lines and provide a new breeding standard of dual-purpose male-sterile lines which promotes the sustainable development of two-lines hybrid rice. [ABSTRACT FROM AUTHOR]

Soil salinity has become a major stress factor that reduces crop productivity worldwide. Sodium (Na+) toxicity in a number of crop plants is tightly linked with shoot Na+ overaccumulation, thus Na+ exclusion from shoot is crucial for salt tolerance in crops. In this study, we identified a member of the high-affinity K+ transport family (HAK), OsHAK12, which mediates shoots Na+ exclusion in response to salt stress in rice. The Oshak12 mutants showed sensitivity to salt toxicity and accumulated more Na+ in the xylem sap, leading to excessive Na+ in the shoots and less Na+ in the roots. Unlike typical HAK family transporters that transport K+, OsHAK12 is a Na+-permeable plasma membrane transporter. In addition, OsHAK12 was strongly expressed in the root vascular tissues and induced by salt stress. These findings indicate that OsHAK12 mediates Na+ exclusion from shoot, possibly by retrieving Na+ from xylem vessel thereby reducing Na+ content in the shoots. These findings provide a unique function of a rice HAK family member and provide a potential target gene for improving salt tolerance of rice. [ABSTRACT FROM AUTHOR]

Potassium (K+) levels in the soil often limit plant growth and development. As a result, crop production largely relies on the heavy use of chemical fertilizers, presenting a challenging problem in sustainable agriculture. To breed crops with higher K+-use efficiency (KUE), we must learn how K+ is acquired from the soil by the root system and transported to the rest of the plant through K+ transporters. In this study, we identified the function of the rice K+ transporter OsHAK8 , whose expression level is downregulated in response to low-K+ stress. When OsHAK8 was disrupted by CRISPR/Cas9-mediated mutagenesis, Oshak8 mutant plants showed stunted growth, especially under low-K+ conditions. Ion content analyses indicated that K+ uptake and root-to-shoot K+ transport were significantly impaired in Oshak8 mutants under low-K+ conditions. As the OsHAK8 gene was broadly expressed in different cell types in the roots and its protein was targeted to the plasma membrane, we propose that OsHAK8 serves as a major transporter for both uptake and root-to-shoot translocation in rice plants. [ABSTRACT FROM AUTHOR]

Rice blast, caused by the fungal pathogen Magnaporthe oryzae (M. oryzae), is one of the most destructive and widespread plant diseases in the world. Utilization of resistance genes in rice breeding is considered to be an effective and economical method to control this disease. To identify new sources of blast resistance, a set of 1160 introgression lines (ILs) containing chromosome segments of Chaling common wild rice (Oryza rufipogon Griff.) in the genetic background of an elite indica rice variety 93‐11 were developed and phenotyped in the blast nursery. Thirty‐three ILs displaying stable blast resistance in three consecutive years were obtained. Among them, one line, IL1043, was subsequently found to be resistant to all of the 28 M. oryzae isolates from different regions through artificial inoculation in greenhouse. By combining bulk segregant analysis coupled with next‐generation sequencing (BSA‐seq) and recessive class analysis (RCA), a major blast resistance gene in IL1043, designated Picl(t), was mapped on rice chromosome 6 flanked by the markers RM527 and Indel6 with an interval of approximately 925 kb, which covers the Pi2/9 locus. These results will facilitate fine mapping and cloning of Picl(t), and the linked markers will further provide a useful tool for rice blast resistance breeding. [ABSTRACT FROM AUTHOR]

Abstract: Genotyping by sequencing (GBS) has been applied to identify genetic markers in crops for trait association and breeding purposes. Here, we applied GBS technology to study a natural population of 270 Indica rice strains, which resulted in identification of 79,545 genomewide single nucleotide polymorphisms. Using these SNPs, we found the close relationship between the 270 Indica rice strains. Furthermore, we tested the feasibility of using these 270 Indica strains in studying important rice traits by analysing the cadmium and other metal accumulation of these strains and correlating the traits with genetic markers. We identified 32 SNPs to be associated with cadmium (Cd) accumulation, explaining 61.25% of the Cd concentration variances in grains. The genetic markers provided here are valuable resources for future rice studies, and further characterization of the candidate loci identified in this study can also aid the development of low Cd‐accumulating rice varieties. [ABSTRACT FROM AUTHOR]

Excessive cadmium (Cd) accumulation in grains of rice (Oryza sativa L.) is a risk to food security. The transporters in the nodes of rice are involved in the distribution of mineral elements including toxic elements to different tissues such as grains. However, the mechanism of Cd accumulation in grains is largely unknown. Here, we report a node-expressed transporter gene, OsCCX2, a putative cation/calcium (Ca) exchanger, mediating Cd accumulation in the grains of rice. Knockout of OsCCX2 caused a remarkable reduction of Cd content in the grains. Further study showed that disruption of this gene led to a reduced root-to-shoot translocation ratio of Cd. Moreover, Cd distribution was also disturbed in different levels of internode and leaf. OsCCX2 is localized to plasma membrane, and OsCCX2 is mainly expressed in xylem region of vascular tissues at the nodes. OsCCX2 might function as an efflux transporter, responsible for Cd loading into xylem vessels. Therefore, our finding revealed a novel Cd transporter involved in grain Cd accumulation, possibly via a Ca transport pathway in the nodes of rice. [ABSTRACT FROM AUTHOR]

Summary Over‐application of potassium (K) fertilizer in fields has a negative impact on the environment. Developing rice varieties with high KUE will reduce fertilizer for sustainable agriculture. However, the genetic basis of KUE in a more diverse and inclusive population remains largely unexplored. Here, we show that the transcription factor OsNAC25 enhances K+ uptake and confers high KUE under low K+ supply. Disruption of OsNAC25 by CRISPR/Cas9‐mediated mutagenesis led to a considerable loss of K+ uptake capacity in rice roots, coupled with reduced K+ accumulation in rice and severe plant growth defects under low‐ K+ conditions. However, the overexpression of OsNAC25 enhanced K+ accumulation by regulating proper K+ uptake capacity in rice roots. Further analysis displayed that OsNAC25 can bind to the promoter of OsSLAH3 to repress its transcription in response to low‐ K+ stress. Nucleotide diversity analyses suggested that OsNAC25 may be selected during japonica populations' adaptation of low K+ tolerance. Natural variation of OsNAC25 might cause differential expression in different haplotype varieties, thus conferring low K+ tolerance in the Hap 1 and Hap 4 ‐carrying varieties, and the japonica allele OsNAC25 could enhance low K+ tolerance in indica variety, conferring great potential to improve indica low K+ tolerance and grain development. Taken together, we have identified a new NAC regulator involved in rice low K+ tolerance and grain development, and provide a potential target gene for improving low K+ tolerance and grain development in rice. [ABSTRACT FROM AUTHOR]

Abstract: Abiotic stress has been shown to limit the growth, development, and productivity of crops. Here, we characterized the function of a rice bZIP transcription factor OsbZIP16 in drought stress. Expression of OsbZIP16 was dramatically induced under drought conditions. Transient expression and transactivation assays demonstrated that OsbZIP16 was localized in the nucleus and had transactivation activity. At both the seedling and tillering stages, transgenic rice plants overexpressing OsbZIP16 exhibited significantly improved drought resistance, which was positively correlated with the observed expression levels of OsbZIP16. Representative downstream drought-inducible genes were observed to have significantly higher expression levels in transgenic rice plants than in the wild type plants under drought conditions. OsbZIP16 was shown to be induced by exogenous ABA treatment, while overexpression of OsbZIP16 was observed to make transgenic plants more sensitive to ABA than wild type plants were. Transcriptome analysis identified a number of differentially expressed genes between wild type plants and plants overexpressing OsbZIP16, many of which are involved in stress response according to their gene ontologies. Overall, our findings suggest that OsbZIP16 positively regulates drought resistance in rice. [Copyright &y& Elsevier]