Rice SDSFL1 plays a critical role in the regulation of plant structure through the control of different phytohormones and altered cell structure.

Semi-dwarfism is one of the most important agronomic traits for many cereal crops. In the present study, a mutant with semi-dwarf and short flag leaf 1, sdsfl1, was identified and characterized. The sdsfl1 mutant demonstrated some distinguished structural alterations, including shorter plant height and flag leaf length, increased tiller numbers and flag leaf width, and decreased panicle length compared with those of wild type (WT). Genetic analysis suggested that the mutant traits were completely controlled by a single recessive gene. The SDSFL1 gene was mapped to the long arm of chromosome 3 within a region of 44.6 kb between InDel markers A3P8.3 and A3P8.4. The DNA sequence analysis revealed that there was only a T to C substitution in the coding region of LOC_Os03g63970, resulting in the substitution of Tryptophan (Try) to Arginine (Arg) and encoding a GA 20 oxidase 1 protein of 372 amino acid residues. Photosynthesis analysis showed that the photosynthetic rate (Pn), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) were significantly increased in sdsfl1. Chlorophyll a (Chl a), total Chl, and carotenoid contents were significantly increased in sdsfl1 compared with those in WT. sdsfl1 carried a reduced level of GA3 but reacted to exogenously applied gibberellins (GA). Moreover, the levels of abscisic acid (ABA), indole 3-acetic acid (IAA), and salicylic acid (SA) were notably improved in sdsfl1, whereas there was no noteworthy change in jasmonic acid (JA). The results thus offer a visible foundation for the molecular and physiological analysis of the SDSFL1 gene, which might participate in various functional pathways for controlling plant height and leaf length in rice breeding.

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

KEY MESSAGE: A rice receptor-like kinase gene OSBBS1/OsRLCK109 was identified; this gene played vital roles in leaf senescence and the salt stress response. Early leaf senescence can cause negative effects on rice yield, but the underlying molecular regulation is not fully understood. bilateral blade senescence 1 (bbs1), 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. bbs1 showed accelerated dark-induced leaf senescence. The OsBBS1 gene was cloned by a map-based cloning strategy, and a guanine (G) insertion was found in the first exon of LOC_Os03g24930. This gene encodes a receptor-like cytoplasmic kinase and was named OsRLCK109 in a previous study. Transgenic LOC_Os03g24930 knockout plants generated by a CRISPR/Cas9 strategy exhibited similar early leaf senescence phenotypes as did the bbs1 mutant, which confirmed that LOC_Os03g24930 was the OsBBS1 gene. OsBBS1/OsRLCK109 was expressed in all detected tissues and was predominantly expressed in the main vein region of mature leaves. The expression of OsBBS1 could be greatly induced by salt stress, and the bbs1 mutant exhibited hypersensitivity to salt stress. In conclusion, this is the first identification of OsRLCKs participating in leaf senescence and playing critical roles in the salt stress response in rice (Oryza sativa L.).

The ferredoxin-dependent glutamate synthase (OsFd-GOGAT) participates in leaf senescence and the nitrogen remobilization in rice.

Ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) plays major roles in photorespiration and primary nitrogen assimilation. However, due to no mutant or knockdown lines of OsFd-GOGAT have been reported in rice (Oryza sativa L.), the contribution of OsFd-GOGAT to rice foliar nitrogen metabolism remains little up-to-date. Here, we isolated a rice premature leaf senescence mutant named gogat1, which was reduced in 67% of the total GOGAT enzyme activity in leaves. The gogat1 mutant exhibited chlorosis under natural condition, while showed less extent premature leaf senescence under low light treatment. The gogat1 locus was mapped to a 54.1 kb region on chromosome 7, and the sequencing of OsFd-GOGAT showed one substitution (A to T) at the 3017th nucleotide of the open reading frame, leading to the amino-acid substitution of leucine changed to histidine. The gogat1 mutant showed reduced seed setting rate, while the grain protein content in gogat1 mutant was significantly higher than that in wild type. Meanwhile, during the grain-filling stage, total amino acids in the up three leaves and the upmost internode were increased dramatically. The results in this study suggested that OsFd-GOGAT might participate in nitrogen remobilization during leaf senescence, which provides a potential way to improve nitrogen use efficiency in rice.