Hydrogen Sulfide And The Heme Oxygenase-1/Carbon Monoxide Signaling System Regulate Lateral Root Formation In Tomato

In recent years, animal research indicated that hydrogen sulfide (H2S), as a novel endogenous gasotransmitter, plays important physiological roles such as anti-inflammatory, metabolic, vasorelaxant, neuroprotective functions. However, the knowledge on the mechanisms of H2S action as a signaling molecule in plant system is still limited. Auxin is the key sensing signal for root development, particularly for lateral root formation, whereas the existing knowledge about auxin controlling lateral root initiation is needed to be developed. Heme oxygenase-1/carbon monoxide (HO-1/CO) signaling system is involved in many physiological activities in plant, but the mechanism of endogenous and exogenous factors inducing this signaling system still requires elucidation. We carried out a series of experiments to address the above issues, and our achievements are listed as follows:1. The HO-1/CO signaling system is involved in H2S-induced tomato (Solanum lycopersicum L.) lateral root formation. Applications of H2S donor sodium hydrosulfide (NaHS), CO aqueous solutiuon or the HO-1 inducer hemin to tomato seedlings up-regulated SlHO-1 transcripts, HO-1 activity, and then accelerated lateral root formation, whereas other catalytic products of HO-1 [biliverdin (BV) and Fe2+] failed to induce the above positive responses. Interestingly, NaHS, hemin and CO could rescue the endogenous H2S scavenger hypotaurine (HT)-induced inhibition to different degrees, while the inhibition triggered by the HO-1-specific inhibitor zinc protoporphyrin IX (ZnPPIX) could not be alleviated by NaHS. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis also suggested that the H2S-induced regulation of cell cycle regulatory genes during lateral root formation, including upregulation of SICDKA;1, SlCYCA2;1, simultaneously with downregulation of SIKRP2, was also significantly reversed by ZnPPIX. To sum up, in our experimental condition, we primarily confirmed that HO-1/CO signaling system is involved in the process of lateral root formation.2. H2S is involved in auxin-induced lateral root development in tomato. This research showed the basipetal auxin transport inhibitor naphthylphthalamic acid (NPA)-induced down-regulation of L-Cysteine desulfhydrase (DES) activity, transcripts of SIDES 1, endogenous H2S contents, and the inhibition of lateral root formation could be alleviated by NaHS. Naphthaleneacetic acid (NAA) or NaHS could simultaneously induce transcripts of SIDES1, DES activity and endogenous H2S contents, and thereafter the stimulation of lateral root formation. However, no additive effects were observed when NAA was co-treated with NaHS (lower than 10 mM) in the induction of lateral root formation. Besides, it was confirmed that H2S or HS-,not the other sulfur-containing components derived from NaHS, was attributed to the stimulative action, indicating that only H2S or HS- contributed to the inducible responses. Furthermore, HT significantly inhibited H2S metabolism and lateral root formation. But the inhibition could be alleviated by NaHS, rather than NAA. Molecular evidence revealed that both NaHS- or NAA-induced modulation of some cell cycle regulatory genes, including the up-regulation of SICDKA;1 and SICYCA2;1, together with simultaneous down-regulation of SlKRP2, were significantly reversed by HT pretreatment. The above results suggested that H2S is at least partially involved in tomato lateral root formation as a gasotransmitter.To sum up, this context provided theoretical basis by biochemical and molecular biological approaches for the possible practice and application of H2S in regulating lateral root formation.