Natural variation in OsSEC13 HOMOLOG 1 modulates redox homeostasis to confer cold tolerance in rice

Overexpression of OsPIN5b Alters Plant Architecture and Impairs Cold Tolerance in Rice (Oryza sativa L.)

Auxin plays a versatile role in regulating plant growth and development. The auxin efflux carrier PIN-FORMED (PIN) proteins dictate the distribution and maximum of auxin within various tissues. Despite extensive research on OsPINs in recent years, their functions in abiotic stress resistance, particularly cold tolerance, remain poorly understood. Here, we investigated the role of OsPIN5b in rice (Oryza sativa L.) growth and development, as well as its contribution to cold tolerance using overexpression technology. Overexpression of OsPIN5b (OE) resulted in reduced shoot height and a lower number of adventitious roots at the seedling stage. Transgenic rice plants exhibited an earlier heading date, stunted growth, and compromised agronomic traits, including shortened panicle length, decreased grain number per panicle, reduced seed size, and lower seed setting rate during the reproductive stage. Auxin content in the transgenic lines was significantly elevated, as indicated by the upregulation of the auxin-responsive gene OsIAA20 and increased auxin levels quantified using a newly developed method. Compared with wild-type plants, the cold tolerance of OE plants was markedly reduced, as evidenced by lower survival rates, higher levels of electrolyte leakage, and increased malondialdehyde (MDA) production following cold treatment. In line with this, the transgenic lines produced less soluble sugar and proline, while accumulating more hydrogen peroxide (H2O2) and superoxide anion radicals (O2-) after cold treatment. Furthermore, the activities of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), were notably decreased upon cold treatment compared with those in WT plants. Additionally, OsRBOHH, which plays a role in ROS production, was significantly upregulated in transgenic lines both before and after chilling stress, suggesting that OsRBOHH plays a potential role in regulating ROS production. Collectively, overexpression of OsPIN5b substantially disturbs auxin homeostasis, resulting in impaired plant architecture and agronomic traits. More importantly, the upregulation of OsPIN5b compromises rice cold tolerance by perturbing ROS homeostasis and adversely influencing the accumulation of soluble sugar and proline.

Analysis of the role of the rice metallothionein gene OsMT2b in grain size regulation

Seed size is one of the three main characteristics determining rice yield. Clarification of the mechanisms regulating seed size in rice has implications for improving rice yield. Although several genes have been reported to regulate seed size, most of the reports are fragmentary. The role of metallothioneins (MTs) in regulating seed size remains unknown. Here, we found that OsMT2b was expressed in both spikelets and developing seeds. OsMT2b-overexpression lines had large and heavy seeds, and RNAi (RNA interference) lines had small and light seeds. Scanning electron microscopy (SEM) observations revealed that OsMT2b regulated spikelet hull size by affecting cell expansion in the outer epidermis. Histological analysis indicated that OsMT2b affected the number of cells in the cross-section of spikelet hulls, which affected seed size. The fresh weight of seeds was consistently higher in OsMT2b-overexpression lines than in seeds of the wild-type (WT) and RNAi lines from 6 DAP (days after pollination) until maturity, indicating that OsMT2b affected seed filling. Reverse transcription-quantitative PCR (RT-qPCR) analyses revealed that OsMT2b regulates the expression of reactive oxygen species scavenging-related genes involved in seed size regulation. In conclusion, our results indicated that OsMT2b positively regulates seed size, which provides a novel approach for regulating seed size with genetic engineering technology.

The OsSRO1c-OsDREB2B complex undergoes protein phase transition to enhance cold tolerance in rice

Cold stress is one of the major abiotic stress factors affecting rice growth and development, leading to significant yield loss in the context of global climate change. Exploring natural variants that confer cold resistance and the underlying molecular mechanism responsible for this is the major strategy to breed cold-tolerant rice varieties. Here, we show that natural variations of a SIMILAR to RCD ONE (SRO) gene, OsSRO1c, confer cold tolerance in rice at both seedling and booting stages. Our in vivo and in vitro experiments demonstrated that OsSRO1c possesses intrinsic liquid-liquid phase-separation ability and recruits OsDREB2B, an AP2/ERF transcription factor that functions as a positive regulator of cold stress, into its biomolecular condensates in the nucleus, resulting in elevated transcriptional activity of OsDREB2B. We found that the OsSRO1c-OsDREB2B complex directly responds to low temperature through dynamic phase transitions and regulates key cold-response genes, including COLD1. Furthermore, we showed that introgression of an elite haplotype of OsSRO1c into a cold-susceptible indica rice could significantly increase its cold resistance. Collectively, our work reveals a novel cold-tolerance regulatory module in rice and provides promising genetic targets for molecular breeding of cold-tolerant rice varieties.

Involvement of the Metallothionein gene OsMT2b in Drought and Cadmium Ions Stress in Rice

Abiotic stress is one of the major factors restricting the production of rice (Oryza sativa L.). Developing rice varieties with dual abiotic stress tolerance is essential to ensure sustained rice production, which is necessary to illustrate the regulation mechanisms underlying dual stress tolerance. At present, only a few genes that regulate dual abiotic stress tolerance have been reported. In this study, we determined that the expression of OsMT2b was induced by both drought and Cd2+ stress. After stress treatment, OsMT2b-overexpression lines exhibited enhanced drought tolerance and better physiological performance in terms of relative water content and electrolyte leakage compared with wild-type (WT). Further analysis indicated that ROS levels were lower in OsMT2b-overexpression lines than in WT following stress treatment, suggesting that OsMT2b-overexpression lines had a stronger ability to scavenge ROS under stress. Reverse transcription-quantitative PCR (RT-qPCR) results demonstrated that under drought stress, OsMT2b influenced the expression of genes involved in ROS scavenging to enhance drought tolerance in rice. In addition, OsMT2b-overexpression plants displayed increased tolerance to Cd2+ stress, and physiological assessment results were consistent with the observed phenotypic improvements. Thus, enhancing ROS scavenging ability through OsMT2b overexpression is a novel strategy to boost rice tolerance to both drought and Cd2+ stress, offering a promising approach for developing rice germplasm with enhanced resistance to the abiotic stressors.

OsEIN2-OsEIL1/2 pathway negatively regulates chilling tolerance by attenuating OsICE1 function in rice

Low temperature severely affects rice development and yield. Ethylene signal is essential for plant development and stress response. Here, we reported that the OsEIN2-OsEIL1/2 pathway reduced OsICE1-dependent chilling tolerance in rice. The overexpressing plants of OsEIN2, OsEIL1 and OsEIL2 exhibited severe stress symptoms with excessive reactive oxygen species (ROS) accumulation under chilling, while the mutants (osein2 and oseil1) and OsEIL2-RNA interference plants (OsEIL2-Ri) showed the enhanced chilling tolerance. We validated that OsEIL1 and OsEIL2 could form a heterxodimer and synergistically repressed OsICE1 expression by binding to its promoter. The expression of OsICE1 target genes, ROS scavenging- and photosynthesis-related genes were downregulated by OsEIN2 and OsEIL1/2, which were activated by OsICE1, suggesting that OsEIN2-OsEIL1/2 pathway might mediate ROS accumulation and photosynthetic capacity under chilling by attenuating OsICE1 function. Moreover, the association analysis of the seedling chilling tolerance with the haplotype showed that the lower expression of OsEIL1 and OsEIL2 caused by natural variation might confer chilling tolerance on rice seedlings. Finally, we generated OsEIL2-edited rice with an enhanced chilling tolerance. Taken together, our findings reveal a possible mechanism integrating OsEIN2-OsEIL1/2 pathway with OsICE1-dependent cascade in regulating chilling tolerance, providing a practical strategy for breeding chilling-tolerant rice.

Integration of molecular breeding and multi-resistance screening for developing a promising restorer line Guihui5501 with heavy grain, good grain quality, and endurance to biotic and abiotic stresses

Rice, a critical staple on a global scale, faces escalating challenges in yield preservation due to the rising prevalence of abiotic and biotic stressors, exacerbated by frequent climatic fluctuations in recent years. Moreover, the scorching climate prevalent in the rice-growing regions of South China poses obstacles to the cultivation of good-quality, heavy-grain varieties. Addressing this dilemma requires the development of resilient varieties capable of withstanding multiple stress factors. To achieve this objective, our study employed the broad-spectrum blast-resistant line Digu, the brown planthopper (BPH)-resistant line ASD7, and the heavy-grain backbone restorer lines Fuhui838 (FH838) and Shuhui527 (SH527) as parental materials for hybridization and multiple crossings. The incorporation of molecular markers facilitated the rapid pyramiding of six target genes (Pi5, Pita, Pid2, Pid3, Bph2, and Wxb ). Through a comprehensive evaluation encompassing blast resistance, BPH resistance, cold tolerance, grain appearance, and quality, alongside agronomic trait selection, a promising restorer line, Guihui5501 (GH5501), was successfully developed. It demonstrated broad-spectrum resistance to blast, exhibiting a resistance frequency of 77.33% against 75 artificially inoculated isolates, moderate resistance to BPH (3.78 grade), strong cold tolerance during the seedling stage (1.80 grade), and characteristics of heavy grains (1,000-grain weight reaching 35.64 g) with good grain quality. The primary rice quality parameters for GH5501, with the exception of alkali spreading value, either met or exceeded the second-grade national standard for premium edible rice varieties, signifying a significant advancement in the production of good-quality heavy-grain varieties in the southern rice-growing regions. Utilizing GH5501, a hybrid combination named Nayou5501, characterized by high yield, good quality, and resistance to multiple stresses, was bred and received approval as a rice variety in Guangxi in 2021. Furthermore, genomic analysis with gene chips revealed that GH5501 possessed an additional 20 exceptional alleles, such as NRT1.1B for efficient nitrogen utilization, SKC1 for salt tolerance, and STV11 for resistance to rice stripe virus. Consequently, the restorer line GH5501 could serve as a valuable resource for the subsequent breeding of high-yielding, good-quality, and stress-tolerant hybrid rice varieties.

Natural variation in STAYGREEN contributes to low-temperature tolerance in cucumber

Low-temperature (LT) stress threatens cucumber production globally; however, the molecular mechanisms underlying LT tolerance in cucumber remain largely unknown. Here, using a genome-wide association study (GWAS), we found a naturally occurring single nucleotide polymorphism (SNP) in the STAYGREEN (CsSGR) coding region at the gLTT5.1 locus associated with LT tolerance. Knockout mutants of CsSGR generated by clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease 9 exhibit enhanced LT tolerance, in particularly, increased chlorophyll (Chl) content and reduced reactive oxygen species (ROS) accumulation in response to LT. Moreover, the C-repeat Binding Factor 1 (CsCBF1) transcription factor can directly activate the expression of CsSGR. We demonstrate that the LT-sensitive haplotype CsSGRHapA , but not the LT-tolerant haplotype CsSGRHapG could interact with NON-YELLOW COLORING 1 (CsNYC1) to mediate Chl degradation. Geographic distribution of the CsSGR haplotypes indicated that the CsSGRHapG was selected in cucumber accessions from high latitudes, potentially contributing to LT tolerance during cucumber cold-adaptation in these regions. CsSGR mutants also showed enhanced tolerance to salinity, water deficit, and Pseudoperonospora cubensis, thus CsSGR is an elite target gene for breeding cucumber varieties with broad-spectrum stress tolerance. Collectively, our findings provide new insights into LT tolerance and will ultimately facilitate cucumber molecular breeding.

Genome-Wide Identification of Catalase Gene Family and the Function of SmCAT4 in Eggplant Response to Salt Stress

Salinity is an important abiotic stress, damaging plant tissues by causing a burst of reactive oxygen species (ROS). Catalase (CAT) enzyme coded by Catalase (CAT) genes are potent in reducing harmful ROS and hydrogen peroxide (H2O2) produced. Herein, we performed bioinformatics and functional characterization of four SmCAT genes, retrieved from the eggplant genome database. Evolutionary analysis CAT genes revealed that they are divided into subgroups I and II. The RT-qPCR analysis of SmCAT displayed a differential expression pattern in response to abiotic stresses. All the CAT proteins of eggplant were localized in the peroxisome, except for SmCAT4, which localized in the cytomembrane and nucleus. Silencing of SmCAT4 compromised the tolerance of eggplant to salt stress. Suppressed expression levels of salt stress defense related genes SmTAS14 and SmDHN1, as well as increase of H2O2 content and decrease of CAT enzyme activity was observed in the SmCAT4 silenced eggplants. Our data provided insightful knowledge of CAT gene family in eggplant. Positive regulation of eggplant response to salinity by SmCAT4 provides resource for future breeding programs.