Abstract
Rice is an important monocotyledonous crop worldwide; it differs from the dicotyledonous plant Arabidopsis in many aspects. In Arabidopsis, ethylene and auxin act synergistically to regulate root growth and development. However, their interaction in rice is still unclear. Here, we report that the transcriptional activation of OsEIL1 on the expression of YUC8/REIN7 and indole-3-pyruvic acid (IPA)-dependent auxin biosynthesis is required for ethylene-inhibited root elongation. Using an inhibitor of YUC activity, which regulates auxin biosynthesis via the conversion of IPA to indole-3-acetic acid (IAA), we showed that ethylene-inhibited primary root elongation is dependent on YUC-based auxin biosynthesis. By screening phenotypes of seedling primary root from mutagenesis libraries following ethylene treatment, we identified a rice ethylene-insensitive mutant, rein7-1, in which YUC8/REIN7 is truncated at its C-terminus. Mutation in YUC8/REIN7 reduced auxin biosynthesis in rice, while YUC8/REIN7 overexpression enhanced ethylene sensitivity in the roots. Moreover, YUC8/REIN7 catalyzed the conversion of IPA to IAA, truncated version at C-terminal end of the YUC8/REIN7 resulted in significant reduction of enzymatic activity, indicating that YUC8/REIN7 is required for IPA-dependent auxin biosynthesis and ethylene-inhibited root elongation in rice early seedlings. Further investigations indicated that ethylene induced YUC8/REIN7 expression and promoted auxin accumulation in roots. Addition of low concentrations of IAA rescued the ethylene response in the rein7-1, strongly demonstrating that ethylene-inhibited root elongation depends on IPA-dependent auxin biosynthesis. Genetic studies revealed that YUC8/REIN7-mediated auxin biosynthesis functioned downstream of OsEIL1, which directly activated the expression of YUC8/REIN7. Thus, our findings reveal a model of interaction between ethylene and auxin in rice seedling primary root elongation, enhancing our understanding of ethylene signaling in rice.
Highlights
Root systems of higher plants play essential roles in absorbing water and nutrients and supporting the plant body
We show that YUC8/REIN7, a member of the YUC gene family, catalyzing the conversion of indole-3-pyruvic acid (IPA) to Indole-3-acetic acid (IAA) in auxin biosynthesis, is transcriptionally modulated by ethylene signaling component OsEIL1, and mainly participates in auxin biosynthesis and ethylene-inhibited root growth
We first identified that ethylene-inhibited root elongation is suppressed by the inhibitor of YUC activity, and YUC8/REIN7 is required for IPA-dependent auxin biosynthesis, indicating that YUC8/REIN7 is involved in ethylene-inhibited root elongation in rice early seedlings
Summary
Root systems of higher plants play essential roles in absorbing water and nutrients and supporting the plant body. Previous studies have shown that auxin biosynthesis, transport and auxin-dependent signaling affect root development [10,11,12]. Indole-3-acetic acid (IAA), the major form of auxin in plants, can be biosynthesized in tryptophan (Trp) -dependent and -independent pathways [13,14]. There are four pathways for IAA biosynthesis from Trp in plants: the YUCCA (YUC) pathway or the indole-3-pyruvic acid (IPA) pathway, the tryptamine (TAM) pathway, the indole-3-acetamide pathway, and the indole-3-acetaldoxime pathway [13]. The diversity of auxin biosynthesis indicates that different pathways may have distinctive roles in plant tissue growth and development
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