Mutation of SPOTTED LEAF4 (SPL4) encoding a microtubule severing protein produces reactive oxygen species (ROS) and delays leaf senescence in rice

Abstract

The mutants show autonomous lesion formation, spontaneous cell death without any pathogen attack and resistance to a pathogen are classified to lesion mimic mutants (LMMs). Through these phenotypes, LMMs were used to study the mechanisms of programmed cell death pathway and response to a pathogen. In this study, the spotted leaf4 (spl4) mutant which is derived from γ-ray irradiation were used to study the spontaneous cell death mechanism. It has been reported that many LMMs its encoding genes were identified but its molecular mechanism of lesion formation and pathogen resistance is still unclear. The reactive oxygen species (ROS) is the product of senescence and ROS can be found near the spots in LMMs during autonomous lesion formation in LMMs even dough it is a developmental stage. Stay-green is the phenomena of delayed senescence and this is the one character that breeders want to achieve. Also, Scientists study this delayed senescence phenotype to elucidate the leaf senescence mechanism. In this study, we analyzed the rice spl4 mutant, which shows autonomous lesion formation on leaf blades, ROS accumulation and shows the stay-green phenotype. The spl4 locus was identified by map-based cloning. This locus encodes a putative microtubule severing protein, spastin. Our data may suggest that the malfunctioning of microtubule severing protein results in pleiotropic phenotypes of autonomous lesion formation, ROS accumulation and delayed senescence in spl4 mutant.