Summary: Heat stress is a major environmental threat affecting crop growth and productivity. However, the molecular mechanisms associated with plant responses to heat stress are poorly understood. Here, we identified a heat stress‐sensitive mutant, hts1, in rice. HTS1 encodes a thylakoid membrane‐localized β‐ketoacyl carrier protein reductase (KAR) involved in de novo fatty acid biosynthesis. Phylogenetic and bioinformatic analysis showed that HTS1 probably originated from streptophyte algae and is evolutionarily conserved in land plants. Thermostable HTS1 is predominantly expressed in green tissues and strongly induced by heat stress, but is less responsive to salinity, cold and drought treatments. An amino acid substitution at A254T in HTS1 causes a significant decrease in KAR enzymatic activity and, consequently, impairs fatty acid synthesis and lipid metabolism in the hts1 mutant, especially under heat stress. Compared to the wild‐type, the hts1 mutant exhibited heat‐induced higher H₂O₂ accumulation, a larger Ca²⁺ influx to mesophyll cells, and more damage to membranes and chloroplasts. Also, disrupted heat stress signaling in the hts1 mutant depresses the transcriptional activation of HsfA2s and the downstream target genes. We suggest that HTS1 is critical for underpinning membrane stability, chloroplast integrity and stress signaling for heat tolerance in rice.

Drought stress is a pivotal environmental factor impacting rice production and presents a significant challenge to sustainable agriculture worldwide. This review synthesizes the latest research advancements in the regulatory mechanisms and signaling pathways that rice employs in response to drought stress. It elaborates on the adaptive changes and molecular regulatory mechanisms that occur in rice under drought conditions. The review highlights the perception and initial transmission of drought signals, key downstream signaling networks such as the MAPK and Ca²⁺ pathways, and their roles in modulating drought responses. Furthermore, the discussion extends to hormonal signaling, especially the crucial role of abscisic acid (ABA) in drought responses, alongside the identification of drought-resistant genes and the application of gene-editing technologies in enhancing rice drought resilience. Through an in-depth analysis of these drought stress regulatory signaling pathways, this review aims to offer valuable insights and guidance for future rice drought resistance breeding and agricultural production initiatives.

Rice (Oryza sativa L.) serves as a staple food for over half the global population, but its cultivation faces significant challenges from abiotic stresses such as drought, salinity, temperature extremes, and heavy metal toxicity. These stresses adversely impact rice growth, yield, and quality, posing a threat to global food security. This review comprehensively explores the physiological, biochemical, and molecular responses of rice to abiotic stresses, highlighting key functional genes and signaling pathways. Advanced breeding strategies, including molecular marker-assisted selection (MAS), genome-wide association studies (GWASs), and CRISPR/Cas9-based genome editing, offer innovative solutions for enhancing stress tolerance. Integrated approaches combining traditional breeding, modern molecular techniques, and exogenous applications such as plant hormones and beneficial microorganisms are discussed. These methods aim to develop rice varieties resilient to multiple stresses, ensuring sustainable production. Future prospects emphasize the integration of multi-omics technologies and the establishment of stress-resistant germplasm banks to accelerate breeding programs. This review provides some support for the development of stress-tolerant rice varieties to help address agricultural challenges in the context of climate change.

Isolation of leaf-color mutants is important in understanding the mechanisms of chloroplast biogenesis and development. In this study, we identified and characterized a rice (Oryza sativa) mutant, yellow leaf 2 (yl2), exhibiting pale yellow leaves with a few longitudinal white stripes at the early seedling stage then gradually turning yellow. Genetic analyses revealed that YL2 encodes a thylakoid membrane-localized protein with significant sequence similarity to UMP kinase proteins in prokaryotes and eukaryotes. Prokaryotic UMP kinase activity was subsequently confirmed, with YL2 deficiency causing a significant reduction in chlorophyll accumulation and photochemical efficiency. Moreover, YL2 is also light dependent and preferentially expressed in green tissues. Chloroplast development was abnormal in the yl2 mutant, possibly due to reduced accumulation of thylakoid membranes and a lack of normal stroma lamellae. 2D Blue-Native SDS-PAGE and immunoblot analyses revealed a reduction in several subunits of photosynthetic complexes, in particular, the AtpB subunit of ATP synthase, while mRNA levels of corresponding genes were unchanged or increased compared with the wild type. In addition, we observed a significant decrease (ca. 36.3%) in cpATPase activity in the yl2 mutant compared with the wild type. Taken together, our results suggest that UMP kinase activity plays an essential role in chloroplast development and regulating cpATPase biogenesis in rice.

Chloroplast ATP synthase (cpATPase) is an importance thylakoid membrane-associated photosynthetic complex involved in the light-dependent reactions of photosynthesis. In this study, we isolated and characterized a rice (Oryza sativa) mutant yellow leaf 1 (yl1), which exhibits chlorotic leaves throughout developmental stages. The YL1 mutation showed reduced chlorophyll contents, abnormal chloroplast morphology and decreased photochemical efficiency. Moreover, YL1 deficiency disrupts the expression of genes associated with chloroplast development and photosynthesis. Molecular and genetic analyses revealed that YL1 is a nucleus-encoded protein with a predicted transmembrane domain in its carboxyl-terminus that is conserved in the higher plant kingdom. YL1 localizes to chloroplasts and is preferentially expressed in green tissues containing chloroplasts. Immunoblot analyses showed that inactivation of YL1 leads to drastically reduced accumulation of AtpA (α) and AtpB (β), two core subunits of CF₁αβ subcomplex of cpATPase, meanwhile, a severe decrease (ca. 41.7%) in cpATPase activity was observed in the yl1-1 mutant compared with the wild type. Furthermore, yeast two-hybrid and bimolecular fluorescence complementation assays revealed a specific interaction between YL1 and AtpB subunit of cpATPase. Taken together, our results suggest that YL1 is a plant lineage-specific auxiliary factor involved in the biogenesis of the cpATPase complex, possibly via interacting with the β-subunit.

The identification of spotted leaf 50 (spl50), a novel lesion mimic mutant (LMM) in rice, provides critical insights into the mechanisms underlying programmed cell death (PCD) and innate immunity in plants. Based on ethyl methane sulfonate (EMS)-induced mutagenesis, the spl50 mutant mimics hypersensitive responses in the absence of pathogen by displaying spontaneous necrotic lesions after the tillering phase. SPL50, an ARM repeat protein essential for controlling reactive oxygen species (ROS) metabolism and boosting resistance to blast disease, was identified by map-based cloning techniques. This work also demonstrates the detrimental effects of spl50 on photosynthetic efficiency and chloroplast development. The crucial significance of SPL50 in cellular signaling and stress response is shown by its localization to the cytoplasm and constitutive expression in various plant tissues. In light of growing concerns regarding global food security, this study highlights the pivotal role of SPL50 in regulating programmed cell death (PCD) and enhancing the immune response in plants, contributing to strategies for improving crop disease resistance. The novel identification of the SPL50 gene in rice, encoding an ARM repeat protein, reveals its pivotal role in regulating PCD and innate immune responses independently of pathogen attack.