A D-cysteine desulfhydrase, SlDCD2, participates in tomato fruit ripening by modulating ROS homoeostasis and ethylene biosynthesis

Hydrogen sulfide(H_(2)S)is involved in multiple processes during plant growth and development.D-cysteine desulfhydrase(DCD)can produce H_(2)S with D-cysteine as the substrate;however,the potential developmental roles of DCD have not been explored during the tomato lifecycle.In the present study,SlDCD2 showed increasing expression during fruit ripening.Compared with the control fruits,the silencing of SlDCD2 by pTRV2-SlDCD2 accelerated fruit ripening.A SlDCD2 gene-edited mutant was constructed by CRISPR/Cas9 transformation,and the mutant exhibited accelerated fruit ripening,decreased H_(2)S release,higher total cysteine and ethylene contents,enhanced chlorophyll degradation and increased carotenoid accumulation.Additionally,the expression of multiple ripening-related genes,including NYC1,PAO,SGR1,PDS,PSY1,ACO1,ACS2,E4,CEL2,and EXP was enhanced during the dcd2 mutant tomato fruit ripening.Compared with the wild-type fruits,SlDCD2 mutation induced H_(2)O_(2) and malondialdehyde(MDA)accumulation in fruits,which led to an imbalance in reactive oxygen species(ROS)metabolism.A correlation analysis indicated that H_(2)O_(2) content was strongly positively correlated with carotenoids content,ethylene content and ripening-related gene expression and negatively correlated with the chlorophyll content.Additionally,the dcd2 mutant showed earlier leaf senescence,which may be due to disturbed ROS homeostasis.In short,our findings show that SlDCD2 is involved in H_(2)S generation and that the reduction in endogenous H_(2)S production in the dcd2 mutant causes accelerated fruit ripening and premature leaf senescence.Additionally,decreased H_(2)S in the dcd2 mutant causes excessive H_(2)O_(2) accumulation and increased ethylene release,suggesting a role of H_(2)S and SlDCD2 in modulating ROS homeostasis and ethylene biosynthesis.

Photocatalyst-controlled and visible light-enabled selective oxidation of pyridinium salts

This study proposes two different methods of photocatalytic-controlled and visible light-induced selective oxidation of pyridiniums with air as the terminal oxidant.The key to these transformations is to choose the appropriate light source and photocatalyst.Pyridiniums are successfully converted into pyrroles through oxygen-mediated cycloaddition,proton-coupled electron transfer(PCET),pyridine ring opening,and recyclization.The other route is that pyridiniums selectively form 4-carbonyl pyridines through free radical rearrangement/aerobic oxidation under the catalysis of cobalt(Ⅱ).