L-cysteine desulfhydrase-related H2S production is involved in OsSE5-promoted ammonium tolerance in roots of Oryza sativa

Previous studies revealed that rice heme oxygenase PHOTOPERIOD SENSITIVITY 5 (OsSE5) is involved in the regulation of tolerance to excess ammonium by enhancing antioxidant defence. In this study, the relationship between OsSE5 and hydrogen sulfide (H2S), a well-known signalling molecule was investigated. Results showed that NH4Cl triggered the induction of L-cysteine desulfhydrase (L-DES)-related H2S production in rice seedling roots. A H2S donor, not only alleviated the excess ammonium-triggered inhibition of root growth, but also reduced endogenous ammonium, both of which were aggravated by the hypotaurine (HT, a H2S scavenger) or DL-propargylglycine (PAG, a L-DES inhibitor). Nitrogen-metabolism related enzymes were activated by H2S, thus resulting in induction of amino acid synthesis and total nitrogen content. Interestingly, activity of L-DES, as well as the enzymes involved in nitrogen metabolism was significantly increased in OsSE5-overexpression line (35S:OsSE5), whereas impaired in OsSE5-knockdown mutant (OsSE5-RNAi). Application of HT/PAG or H2S donor could differentially block or rescue NH4Cl-hyposensitivity or hypersensitivity phenotypes in 35S:OsSE5-1 or OsSE5-RNAi-1 plants, with a concomitant modulation of nitrogen assimilation. Taken together, these results illustrated that H2S function as an indispensable positive regulator participated in OsSE5-promoted ammonium tolerance, in which nitrogen metabolism was facilitated.