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.