Identification Of Two Leaf Early Senescence Mutants,es2 And G1029,and Gene Mapping Of Es2 In Rice

Leaf senescence is the final stage of leaf development in plant.Different actions from the cellular,tissues,and organs are under controlling of highly elaborate genetic program.Early senescence has negative impact on crop productivity,especially in rice.In this study,two leaf senescence mutant lines,es2 and g1029,generated by ethyl methanesulfonate（EMS）mutagenesis were identified.The main results showed as follows:1.es2 senescence symptom appeared at the late tillering stage and coincidence with elevated level of cell death,sugar content,and senescence-associated genes（SAGs）transcription.Anthocyanin content had increased in es2 accompanied with elevated of oxidative stress such as H₂O₂.Oxidative stress byproducts such as malondialdehyde（MDA）,and reactive oxygen species（ROS）content were increased in es2 while protein content was decreased.Chloroplast ultrastructure of es2 was filled with higher in number and larger in size of starch granule and osmophilic plastoglobuli with irregular thylakoid and degrading chloroplast membrane.At the heading stage,es2 exhibited sharply decreased of photosynthetic rate.Moreover,es2 photosynthetic rate was significantly lower than wild type in flag leaf,the second leaf from top,and the third leaf from top.Using map-based cloning technique,we identified that the target gene was anchored between RM12538 and RM12729 on the short arm of chromosome 2.Previously,leaf senescence-related gene has never been reported within this region.This research provides a novel early senescence mutant.2.Another EMS mediated CLJ-derived early leaf senescence mutant,g1029,was identified.The g1029 mutant exhibits early senescence at tillering stage.Evans blue staining elucidated that g1029 leaf suffers cell death.DAB staining elucidated that H₂O₂accumulation was higher in g1029.Increased soluble sugar and anthocyanin content along with increased oxidative stress support leaf senescence trait.In g1029,seed setting rate and1000-grain weight were lower compare to wild type.This study offers leaf senescence mutant and a number of techniques were employed to interpret the result.Many results are in correspondence to previous studies,suggesting that these parameters are useful and reliable methods to study leaf senescence.