Interaction Between HY1 And H₂O₂ In Auxin-Induced Arabidopsis Lateral Root Formation

Haem oxygenase (HO) and hydrogen peroxide (H2O2) are ubiquitously identified as essential components of plant signal transduction system. Their roles in response to various environmental stimuli have been well demonstrated. Our pharmacological results previously revealed that HO-1 is involved in auxin-induced LR formation. H2O2 is also required for auxin-induced adventitious root formation. However, there is no direct report about whether H2O2 is involved in auxin-induced LR formation. Meanwhile, the inter-relationship between HO-1 and H2O2 in auxin-mediated LR development is largely unclear. Present study showed that:1. HY1 is involved in auxin-induced LR formation. Here, we found among various Arabidopsis heme oxygenases, HY1 was the major functional gene involved in lateral root formation. HY1 mutant (hyl-100) showed significant reduced LR formation in normal condition compared with wild-type, whereas the other three HO mutants (ho2, ho3, ho4) not. Additionally, both haemin (a potent inducer of HO-1) and CORM-2 (donor of CO, which is the product of HO) had obvious inducible effect on lateral root formation. NAA could stimulate increase in HY1 transcripts and lateral root formation, while addition of HO-1 specific inhibitor Znpp blocked these effects. Furthermore, hy1-100 showed less sensitivity to NAA treatment compared with wild-type, forming less and shorter lateral root.2. NAA-induced HY1 expression and LR formation are dependent on H2O2. Application of hydrogen peroxide (H2O2) scavenger ascorbic acid (AsA) or dimethylthiourea (DMTU) reversed NAA-induced HY1 expression and lateral root formation, suggesting that H2O2 may involve in above signaling. H2O2 treated alone increased HY1 expression and lateral root formation, application of Znpp reversed these effects, and hy1-100 reduced sensitivity to H2O2 compared with wild-type. These results indicated the inducible effects of auxin on HY1 expression and lateral root formation were dependent on H2O2.3. HYl is required in NAA-induced H2O2 generation and LR formation. Similar to NAA, haemin could also increase H2O2 generation and lateral root formation in wild-type, while Znpp inhibited NAA-induced H2O2 production and lateral root formation. Meanwhile, CORM-2 effectively induced H2O2 generation and lateral root formation, both of which were declined by DMTU.4. Moreover, both CORM-2 and H2O2 reversed inhibition of LR primordia by NPA. CORM-2 and H2O2 regulated cell cycle genes expression in a similar way with NAA, and the effects of NAA, H2O2 and CORM-2 were declined by Znpp or DMTU respectively, confirming that H2O2 and CO were important in early lateral root initiation.In summary, our pharmacological, genetic, and molecular evidence demonstrated an interaction between HY1 and H2O2 existing in auxin-induced Arabidopsis lateral root formation...