Abstract
Auxin is essential for root development, and its regulatory action is exerted at different steps from perception of the hormone up to transcriptional regulation of target genes. In legume plants there is an overlap between the developmental programs governing lateral root and N2-fixing nodule organogenesis, the latter induced as the result of the symbiotic interaction with rhizobia. Here we report the characterization of a member of the L. japonicus TIR1/AFB auxin receptor family, LjAFB6. A preferential expression of the LjAFB6 gene in the aerial portion of L. japonicus plants was observed. Significant regulation of the expression was not observed during the symbiotic interaction with Mesorhizobium loti and the nodule organogenesis process. In roots, the LjAFB6 expression was induced in response to nitrate supply and was mainly localized in the meristematic regions of both primary and lateral roots. The phenotypic analyses conducted on two independent null mutants indicated a specialized role in the control of primary and lateral root elongation processes in response to auxin, whereas no involvement in the nodulation process was found. We also report the involvement of LjAFB6 in the hypocotyl elongation process and in the control of the expression profile of an auxin-responsive gene.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
In order to explore and compare the role played by auxin signaling pathways on root and nodule development in legume plants, we retrieved the L. japonicus TIR1/AFB
To the best of our knowledge, no members of the AFB6 clade have been characterized in plants, and we started our characterization of the L. japonicus family with LotjaGi4g1v0048600.1, hereafter termed LjAFB6
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The major form of auxin in vascular plants, indole-3-acetic acid (IAA), is mainly biosynthesized in aerial tissue and directionally transported to its responsive sink sites, resulting in modulation of local auxin distribution that regulates most aspects of plant growth, development and acclimation [1]. Auxin accumulates at the root tip and afterwards is transported shootward via the lateral root cap and epidermis with a “reverse fountain” transport mechanism [2]. A sophisticated network of signaling pathways is involved in the control of the amount of auxin perceived at the subcellular, cellular, tissue and organ scales
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