NADPH Oxidase RbohD and Ethylene Signaling are Involved in Modulating Seedling Growth and Survival Under Submergence Stress
Chen-Pu Hong | Mao-Chang Wang | Chin-Ying Yang
In higher plants under low oxygen or hypoxic conditions, the phytohormone ethylene and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) are involved in complex regulatory mechanisms in hypoxia signaling pathways. The respiratory burst oxidase homolog D (RbohD), an NADPH oxidase, is involved in the primary stages of hypoxia signaling, modulating the expression of downstream hypoxia-inducible genes under hypoxic stress. In this study, our data revealed that under normoxic conditions, seed germination was delayed in the <i>rbohD</i>/<i>ein2-5</i> double mutant, whereas postgermination stage root growth was promoted. Under submergence, the <i>rbohD/ein2-5</i> double mutant line had an inhibited root growth phenotype. Furthermore, chlorophyll content and leaf survival were reduced in the <i>rbohD/ein2-5</i> double mutant compared with wild-type plants under submerged conditions. In quantitative RT-PCR analysis, the induction of <i>Ethylene-responsive factor 73</i>/<i>hypoxia responsive 1</i> (<i>AtERF73/HRE1</i>) and <i>alcohol dehydrogenase 1</i> (<i>AtADH1</i>) transcripts was lower in the <i>rbohD/ein2-5</i> double mutant during hypoxic stress than in wild-type plants and in <i>rbohD</i> and <i>ein2-5</i> mutant lines. Taken together, our results indicate that an interplay of ethylene and RbohD is involved in regulating seed germination and post-germination stages under normoxic conditions. Moreover, ethylene and RbohD are involved in modulating seedling root growth, leaf chlorophyll content, and hypoxia-inducible gene expression under hypoxic conditions.
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