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.

Clade A type 2 C protein phosphatases (PP2CAs) are core regulatory factors in the plant abscisic acid (ABA) signaling pathway. They play crucial roles in response to abiotic stress. However, a comprehensive understanding of the functions of individual members of rice PP2CA gene families remains limited. This study investigates the role of OsPP2C68 in response to abiotic stress. Our findings indicated that the OsPP2C68 is highly expressed in the embryo and endosperm, and is subcellular localized in the nucleus. OsPP2C68 knockout mutants reduced seed germination and root and stem lengths under ABA treatment. The mutants also exhibited higher stomatal closure rates, indicating increased sensitivity to ABA. In addition, the OsPP2C68 knockout mutants exhibited altered synthesis of osmolytes and antioxidant enzymes under drought and high salinity stress, along with the differential expression of genes associated with drought and salt stress responses, enhancing rice tolerance to drought and salt. These results collectively identify OsPP2C68 as a negative regulator in the rice ABA signaling pathway. It is responsive to drought and salt stress, and involved in regulating stomatal movement.

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.

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.