Hydrogen sulfide acts downstream of methane to induce cucumber adventitious root development.

Previous results have shown that hydrogen sulfide (H2S), mainly catalyzed by l-cysteine desulfhydrase (DES) in plants, triggers adventitious rooting. The objective of this study was to test whether H2S is involved in methane (CH4)-induced adventitious root development in cucumber explants. First, we observed that the activities of DES, endogenous H2S production, and thereafter adventitious root development were induced by CH4 and NaHS (an H2S donor). Some responses were sensitive to hypotaurine (HT; a scavenger of H2S), showing that endogenous H2S production and adventitious rooting were obviously blocked. The development of adventitious root primordia was also impaired. Further molecular evidence revealed that CH4-induced gene expression of CsDNAJ-1, CsCDPK1, CsCDPK5, CsCDC6 (a cell-division-related gene), CsAux22D-like, and CsAux22B-like (two auxin-signaling genes), several molecular markers responsible for adventitious rooting, were blocked by the co-treatment with HT. The occurrence of CH4-elicited S-sulfhydration during the above responses was also sensitive to the removal of endogenous H2S, suggesting the requirement of H2S. Taken together, our results reveal a vital role of endogenous H2S in CH4-triggered cucumber adventitious root development, and thus provide a comprehensive window into the complex signaling transduction pathway in CH4-mediated root organogenesis.

Nitric oxide is involved in methane-induced adventitious root formation in cucumber.

Our previous studies revealed that methane (CH4 ) induces adventitious rooting in cucumber. However, the corresponding molecular mechanism is still elusive. In this work, we discovered that CH4 triggered the accumulation of nitric oxide (NO) and thereafter cucumber adventitious rooting, mimicking the inducing effects of sodium nitroprusside (SNP) and NONOate (two NO-releasing compounds). Above mentioned responses were sensitive to NO scavenger(s), showing that the accumulation of NO and adventitious root development were respectively impaired. Inhibitor test and biochemical analysis suggested that endogenous NO mainly produced by mammalian NO synthase-like enzyme and diamine oxidases (DAO), might be required for adventitious root formation elicited by CH4 . Molecular evidence confirmed that CH4 -mediated induction of several marker genes responsible for adventitious root development, including CsDNAJ-1, CsCDPK1, CsCDPK5, cell division-related gene CsCDC6, and two auxin signaling genes, CsAux22D-like and CsAux22B-like, was casually dependent on NO signaling. The possible involvement of S-nitrosylation during the mentioned CH4 responses was preliminarily illustrated. Taken together, through pharmacological, anatomical and molecular approaches, it is suggested that NO might be involved in CH4 -induced cucumber adventitious rooting, and CH4 -eliciated NO-targeted proteins might be partially modulated at transcriptional and post-translational levels. Our work may increase the understanding of the mechanisms underlying CH4 -elicited root organogenesis in higher plants.