Phenotypic characterization and fine mapping of mps1,a premature leaf senescence mutant in rice （Oryza sativa L.）

Leaves play a key role in photosynthesis in rice plants. The premature senescence of such plants directly reduces the accumulation of photosynthetic products and also affects yield and grain quality significantly and negatively. A novel premature senescence mutant, mps1（mid-late stage premature senescence 1）, was identified from a mutant library consisting of ethyl methane sulfonate（EMS） induced descendants of Jinhui 10, an elite indica restorer line of rice. The mutant allele, mps1, caused no phenotypic differences from the wild type（WT）, Jinhui 10, but drove the leaves to turn yellow when mutant plants grew to the tillering stage, and accelerated leaf senescence from the filling stage to final maturation. We characterized the agronomic traits, content of photosynthetic pigments and photosynthetic efficiency of mps1 and WT, and fine-mapped MPS1. The results showed that the MPS1-drove premature phenotype appeared initially on the leaf tips at the late tillering stage and extended to the middle of leaves during the maturing stage. Compared to the WT, significant differences were observed among traits of the number of grains per panicle（–31.7%） and effective number of grains per panicle（–38.5%） of mps1 individuals. Chlorophyll contents among the first leaf from the top（Top 1st）, the second leaf from the top（Top 2nd） and the third leaf from the top（Top 3rd） of mps1 were significantly lower than those of WT（P〈0.05）, and the levels of photosynthetic efficiency from Top 1st to the forth leaf from the top（Top 4th） of mps1 were significantly lower than those of WT（P〈0.01）. Results from the genetic analysis indicated that the premature senescence of mps1 is controlled by a recessive nuclear gene, and this locus, MPS1 is located in a 37.4-kb physical interval between the markers Indel145 and Indel149 on chromosome 6. Genomic annotation suggested eight open reading frames（ORFs） within this physical region. All of these results will provide informative references for the further researches involving functional analyses and molecular mechanism exploring of MPS1 in rice.