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

Abstract

Hydrogen sulfide (H₂S), 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 H₂S-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. <i>LCD1</i> mutation caused earlier leaf senescence, whereas <i>LCD1</i> overexpression significantly delayed leaf senescence compared with the wild type in 10-week tomato seedlings. Moreover, <i>LCD1</i> overexpression was found to delay dark-induced senescence in detached tomato leaves, and the <i>lcd1</i> mutant showed accelerated senescence. An increasing trend of H₂S production was observed in leaves during storage in darkness, while <i>LCD1</i> deletion reduced H₂S production and <i>LCD1</i> overexpression produced more H₂S compared with the wild-type control. Further investigations showed that <i>LCD1</i> 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 <i>NYC1</i>, <i>PAO</i>, <i>PPH</i>, <i>SGR1</i>, and <i>senescence-associated genes</i> (<i>SAGs</i>) during senescence was attenuated by <i>LCD1</i> overexpression, whereas <i>lcd1</i> mutants showed enhanced senescence-related parameters. Moreover, a correlation analysis indicated that chlorophyll content was negatively correlated with H₂O₂ and malondialdehyde (MDA) content, and also negatively correlated with the expression of chlorophyll degradation-related genes and <i>SAGs</i>. Therefore, these findings increase our understanding of the physiological functions of the H₂S-generating enzyme LCD1 in regulating leaf senescence in tomato.