Drought is a major adverse environmental factor that plants face in nature but the molecular mechanism by which plants transduce stress signals and further endow themselves with tolerance remains unclear. Malectin/malectin-like domains containing receptor-like kinases (MRLKs) have been proposed to act as receptors in multiple biological signaling pathways, but limited studies show their roles in drought stress signaling and tolerance. In this study, we demonstrate OsMRLK63 in rice (Oryza sativa L.) functions in drought tolerance by acting as the receptor of two rapid alkalization factors, OsRALF45 and OsRALF46. We show OsMRLK63 is a typical receptor-like kinase that positively regulates drought tolerance and reactive oxygen species production. OsMRLK63 interacts with and phosphorylates several NADPH oxidases with the primarily phosphorylated site at Ser26 in the N-terminal of RESPIRATORY BURST OXIDASE HOMOLOGUE A (OsRbohA). The application of the two small signal peptides (OsRALF45/46) on rice can greatly alleviate the dehydration of plants induced by mimic drought. This function depends on the existence of OsMRLK63 and the NADPH oxidase-dependent ROS production. The two RALFs interact with OsMRLK63 by binding to its extracellular domain, suggesting they may act as drought/dehydration signal sensors for the OsMRLK63-mediated process. Our study reveals a OsRALF45/46-OsMRLK63-OsRbohs module which contributes to drought stress signaling and tolerance in rice.

Carbohydrate-binding malectin/malectin-like domain-containing proteins (CBMs) are a recently identified protein subfamily of lectins that participates various functional bioprocesses in the animal, bacterial, and plant kingdoms. However, little is known the roles of CBMs in rice development and stress response. In this study, OsCBM1, which encodes a protein containing only one malectin-like domain, was cloned and characterized. OsCBM1 is localized in both the endoplasmic reticulum and plasma membrane. Its transcripts are dominantly expressed in leaves and could be significantly stimulated by a number of phytohormone applications and abiotic stress treatments. Overexpression of OsCBM1 increased drought tolerance and reactive oxygen species production in rice, whereas the knockdown of the gene decreased them. OsCBM1 physically interacts with OsRbohA, a NADPH oxidase, and the expression of OsCBM1 in osrbohA, an OsRbohA-knockout mutant, is significantly downregulated under both normal growth and drought stress conditions. Meanwhile, OsCBM1 can also physically interacts with OsRacGEF1, a specific guanine nucleotide exchange factor for the Rop/Rac GTPase OsRac1, and transient coexpression of OsCBM1 with OaRacGEF1 significantly enhanced ROS production. Further transcriptome analysis showed that multiple signaling regulatory mechanisms are involved in the OsCBM1-mediated processes. All these results suggest that OsCBM1 participates in NADPH oxidase-mediated ROS production by interacting with OsRbohA and OsRacGEF1, contributing to drought stress tolerance of rice. Multiple signaling pathways are likely involved in the OsCBM1-mediated stress tolerance in rice.

NARROW LEAF 1 ( NAL1 ), originally identified for its role in shaping leaf morphology, plant architecture, and various agronomic traits in rice, has remained enigmatic in terms of the molecular mechanisms governing its multifaceted functions. In this study, we present a comprehensive structural analysis of NAL1 proteins, shedding light on how NAL1 regulates the phase separation of its physiological substrate, FRIZZY PANICLE (FZP), a transcription factor. We determined that NAL1 assembles as a hexamer and forms a molecular cage with a wide central channel and three narrower lateral channels, which could discriminate its different substrates into the catalytic sites. Most notably, our investigation unveils that FZP readily forms molecular condensates via phase separation both in vitro and in vivo. NAL1 fine-tunes FZP condensation, maintaining optimal concentrations to enhance transcriptional activity. While phase separation roles include sequestration and suppression of transcriptional or enzymatic activity, our study highlights its context-dependent contribution to transcriptional regulation. NAL1 assumes a pivotal role in regulating the states of these molecular condensates through its proteolytic activity, subsequently enhancing transcriptional cascades. Our findings offer insights into comprehending the molecular mechanisms underpinning NAL1’s diverse functions, with far-reaching implications for the field of plant biology. Additionally, these insights provide valuable guidance for the development of rational breeding strategies aimed at enhancing crop productivity.

Respiratory burst oxidase homolog (RBOH)–based ROS production was widely verified playing vital roles in plant stress responses; however, its inhibitory mechanism remains largely unknown. Here, we demonstrate that a calmodulin-like (CML) protein OsCML27 functions as a flexible brake of OsRbohB-mediated ROS production to regulate rice drought tolerance via an OsMRLK63-OsCML27-OsRbohB module. OsCML27 negatively regulates drought tolerance of rice where the overexpression lines showed a faster water loss rate and a lower survival rate under drought, while the oscml27 mutants exhibited a slower dehydration rate and a slightly lower survival rate as compared to wild type. OsCML27 can interact with and be phosphorylated by a receptor-like kinase OsMRLK63 primarily at Ser ¹¹ , and the phosphorylation level could be increased by drought. The phosphorylation by OsMRLK63 enhances OsCML27 stability, and OsCML27 inhibits ROS production by interacting with OsRbohB in the Ca ²⁺ -dependent manner. All these results reveal that OsCML27 integrates phosphorylation and Ca ²⁺ signals to regulate drought tolerance of rice by fine-tuning OsRbohB-mediated ROS signaling.

The muscat aroma of grape is largely determined by terpenoid volatiles. However, its genetic basis in ‘Muscat Hamburg’ remains unclear. We performed comparative volatile metabolomics between ‘Muscat Hamburg’ and ‘Red Globe’ across berry development, identifying 127 differentially abundant metabolites, with upregulated ones enriched in the monoterpenoid pathway. Using an F1 segregating population (264 progeny), we quantified four key monoterpenoids (α-terpineol, linalool, geraniol, and cis-linalool oxide) over two consecutive years. Using a high-density genetic map with 7872 SNP markers generated via SLAF-seq, we detected stable major QTLs for α-terpineol, linalool, and geraniol on LG5, and a novel QTL for cis-linalool oxide on LG14. Expression analysis revealed that the transcript levels of VvDXS and VvGGPPS1 were significantly higher in ‘Muscat Hamburg’ than in ‘Red Globe’ at ripening. Heterologous overexpression in tomato enhanced terpenoid aroma accumulation without affecting fruit development. These results indicate that VvDXS and VvGGPPS1 play a crucial role in the formation of the aroma in the ‘Muscat Hamburg’ variety.