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. 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 H2S production was observed in leaves during storage in darkness, while LCD1 deletion reduced H2S production and LCD1 overexpression produced more H2S 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 H2O2 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 H2S-generating enzyme LCD1 in regulating leaf senescence in tomato.
Highlights
Leaf senescence represents the final stage of leaf development, which is a genetically controlled process [1]
To elucidate the possible involvement of LCD1 in regulating leaf senescence, two previously reported tomato lines, lcd1-7 and lcd1-9, with mutations near the PAM sequence were used as lcd1 mutants, and two lines with an increased expression of LCD1 under the control of the CaMV 35S promoter were used
H2S production was evaluated by lead acetate H2S detection strips, and the results showed that lcd1 leaves produced less H2S and LCD1 overexpression produced more H2S (Figure 1C)
Summary
Leaf senescence represents the final stage of leaf development, which is a genetically controlled process [1]. The decomposition of chloroplast is initiated, accompanied by the catabolism of macromolecules including nucleic acids, proteins, and lipids. Chloroplasts constitute approximately 70% of the total proteins in green leaves and chlorophyll degradation causes the first visible signs of leaf senescence [3]. The coordinated degradation of chlorophyll is crucial for the breakdown of chloroplasts. Chlorophyll b has to be converted to chlorophyll a before it can be processed into the degradation pathway and NON-YELLOW COLORING 1 (NYC1) catalyzes the reduction of chlorophyll b to 7-hydroxymethyl chlorophyll a [5]. Chlorophyll a is further decomposed to pheophytin a by Mg-dechelatase NON-YELLOWINGs/STAYGREENs (NYEs/SGRs) [6]. Hundreds of senescence-associated genes (SAGs), whose transcripts increase as leaves age [8,9], are involved in the regulation of leaf senescence
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