A guanine insert in <italic>OsBBS1</italic> leads to early leaf senescence and salt stress sensitivity in rice (<italic>Oryza sativa</italic> L.).

Key message: A rice receptor-like kinase gene <italic>OSBBS1</italic>/<italic>OsRLCK109</italic> was identified; this gene played vital roles in leaf senescence and the salt stress response.Abstract: Early leaf senescence can cause negative effects on rice yield, but the underlying molecular regulation is not fully understood. <italic>bilateral blade senescence 1</italic> (<italic>bbs1</italic>), an early leaf senescence mutant with a premature senescence phenotype that occurs mainly performing at the leaf margins, was isolated from a rice mutant population generated by ethylmethane sulfonate (EMS) treatment. The mutant showed premature leaf senescence beginning at the tillering stage and exhibited severe symptoms at the late grain-filling stage. <italic>bbs1</italic> showed accelerated dark-induced leaf senescence. The <italic>OsBBS1</italic> gene was cloned by a map-based cloning strategy, and a guanine (G) insertion was found in the first exon of <italic>LOC_Os03g24930</italic>. This gene encodes a receptor-like cytoplasmic kinase and was named <italic>OsRLCK109</italic> in a previous study. Transgenic <italic>LOC_Os03g24930</italic> knockout plants generated by a CRISPR/Cas9 strategy exhibited similar early leaf senescence phenotypes as did the <italic>bbs1</italic> mutant, which confirmed that <italic>LOC_Os03g24930</italic> was the <italic>OsBBS1</italic> gene. <italic>OsBBS1</italic>/<italic>OsRLCK109</italic> was expressed in all detected tissues and was predominantly expressed in the main vein region of mature leaves. The expression of <italic>OsBBS1</italic> could be greatly induced by salt stress, and the <italic>bbs1</italic> mutant exhibited hypersensitivity to salt stress. In conclusion, this is the first identification of <italic>OsRLCKs</italic> participating in leaf senescence and playing critical roles in the salt stress response in rice (<italic>Oryza sativa</italic> L.). [ABSTRACT FROM AUTHOR]