Roles of a Cysteine Desulfhydrase LCD1 in Regulating Leaf Senescence in Tomato

Hydrogen sulfide (H(2)S), a novel gasotransmitter in both mammals and plants, plays important roles in plant development and stress responses. Leaf senescence represents the final stage of leaf development. The role of H(2)S-producing enzyme L-cysteine desulfhydrase in regulating tomato leaf senescence is still unknown. In the present study, the effect of an L-cysteine desulfhydrase LCD1 on leaf senescence in tomato was explored by physiological analysis. LCD1 mutation caused earlier leaf senescence, whereas LCD1 overexpression significantly delayed leaf senescence compared with the wild type in 10-week tomato seedlings. Moreover, LCD1 overexpression was found to delay dark-induced senescence in detached tomato leaves, and the lcd1 mutant showed accelerated senescence. An increasing trend of H(2)S production was observed in leaves during storage in darkness, while LCD1 deletion reduced H(2)S production and LCD1 overexpression produced more H(2)S compared with the wild-type control. Further investigations showed that LCD1 overexpression delayed dark-triggered chlorophyll degradation and reactive oxygen species (ROS) accumulation in detached tomato leaves, and the increase in the expression of chlorophyll degradation genes NYC1, PAO, PPH, SGR1, and senescence-associated genes (SAGs) during senescence was attenuated by LCD1 overexpression, whereas lcd1 mutants showed enhanced senescence-related parameters. Moreover, a correlation analysis indicated that chlorophyll content was negatively correlated with H(2)O(2) and malondialdehyde (MDA) content, and also negatively correlated with the expression of chlorophyll degradation-related genes and SAGs. Therefore, these findings increase our understanding of the physiological functions of the H(2)S-generating enzyme LCD1 in regulating leaf senescence in tomato.