摘要
Leaf senescence, a type of programmed cell death （PCD） characterized by chlorophyll degradation, is important to plant growth and crop productivity. It emerges that autophagy is involved in chloroplast degradation during leaf senescence. However, the molecular mechanism（s） involved in the process is not well understood. In this study, the genetic and physiological characteristics Of the rice rlsl （rapid leaf senescence 1） mutant were identified. The rlsl mutant developed small, yellow-brown lesions resembling disease scattered over the whole surfaces of leaves that displayed earlier senescence than those of wild-type plants. The rapid loss of chlorophyll content during senescence was the main cause of accelerated leaf senescence in rlsl. Microscopic observation indicated that PCD was misregulated, probably resulting in the accelerated degradation of chloroplasts in rlsl leaves. Map-based cloning of the RLS1 gene revealed that it encodes a pre- viously uncharacterized NB （nucleotide-binding site）-containing protein with an ARM （armadillo） domain at the carboxyl terminus. Consistent with its involvement in leaf senescence, RLS1 was up-regulated during dark-induced leaf senescence and down-regulated by cytokinin. Intriguingly, constitutive expression of RLS1 also slightly accelerated leaf senescence with decreased chlorophyll content in transgenic rice plants. Our study identified a previously uncharacterized NB-ARM protein involved in PCD during plant growth and development, providing a unique tool for dissecting possible autophagy- mediated PCD during senescence in plants.
Leaf senescence, a type of programmed cell death （PCD） characterized by chlorophyll degradation, is important to plant growth and crop productivity. It emerges that autophagy is involved in chloroplast degradation during leaf senescence. However, the molecular mechanism（s） involved in the process is not well understood. In this study, the genetic and physiological characteristics Of the rice rlsl （rapid leaf senescence 1） mutant were identified. The rlsl mutant developed small, yellow-brown lesions resembling disease scattered over the whole surfaces of leaves that displayed earlier senescence than those of wild-type plants. The rapid loss of chlorophyll content during senescence was the main cause of accelerated leaf senescence in rlsl. Microscopic observation indicated that PCD was misregulated, probably resulting in the accelerated degradation of chloroplasts in rlsl leaves. Map-based cloning of the RLS1 gene revealed that it encodes a pre- viously uncharacterized NB （nucleotide-binding site）-containing protein with an ARM （armadillo） domain at the carboxyl terminus. Consistent with its involvement in leaf senescence, RLS1 was up-regulated during dark-induced leaf senescence and down-regulated by cytokinin. Intriguingly, constitutive expression of RLS1 also slightly accelerated leaf senescence with decreased chlorophyll content in transgenic rice plants. Our study identified a previously uncharacterized NB-ARM protein involved in PCD during plant growth and development, providing a unique tool for dissecting possible autophagy- mediated PCD during senescence in plants.
基金
This work was supported by grants from the National Natural Science Foundation of China，the National Key Basic Research and Development Program
