PLENTY, a hydroxyproline O-arabinosyltransferase, negatively regulates root nodule symbiosis in Lotus japonicus.

Emiko Yoro,Masayoshi Kawaguchi,Yoshikatsu Matsubayashi,Takuya Suzaki,Chie Yoshida,Mari Ogawa-Ohnishi,Hanna Nishida

doi:10.1093/jxb/ery364

Abstract

Legumes can survive in nitrogen-deficient environments by forming root-nodule symbioses with rhizobial bacteria; however, forming nodules consumes energy, and nodule numbers must thus be strictly controlled. Previous studies identified major negative regulators of nodulation in Lotus japonicus, including the small peptides CLAVATA3/ESR (CLE)-RELATED-ROOT SIGNAL1 (CLE-RS1), CLE-RS2, and CLE-RS3, and their putative major receptor HYPERNODULATION AND ABERRANT ROOT FORMATION1 (HAR1). CLE-RS2 is known to be expressed in rhizobia-inoculated roots, and is predicted to be post-translationally arabinosylated, a modification essential for its activity. Moreover, all three CLE-RSs suppress nodulation in a HAR1-dependent manner. Here, we identified PLENTY as a gene responsible for the previously isolated hypernodulation mutant plenty. PLENTY encoded a hydroxyproline O-arabinosyltransferase orthologous to ROOT DETERMINED NODULATION1 in Medicago truncatula. PLENTY was localized to the Golgi, and an in vitro analysis of the recombinant protein demonstrated its arabinosylation activity, indicating that CLE-RS1/2/3 may be substrates for PLENTY. The constitutive expression experiments showed that CLE-RS3 was the major candidate substrate for PLENTY, suggesting the substrate preference of PLENTY for individual CLE-RS peptides. Furthermore, a genetic analysis of the plenty har1 double mutant indicated the existence of another PLENTY-dependent and HAR1-independent pathway negatively regulating nodulation.

Highlights

Legumes have evolved the ability to make specialized root organs called nodules, in which nitrogen-fixing symbionts, rhizobial bacteria, reside
We previously reported that the plenty locus is located between markers TM0002 and TM0324 on the long arm of chromosome II in L. japonicus.We narrowed down the region of interest using map-based cloning utilizing a larger mapping population of 1087 F2 plants (Supplementary Fig. S1)
We cloned LjPLENTY, an ortholog of MtRDN1 and PsNOD3, and a homolog of the three AtHPAT genes, and found that, like its orthologs, LjPLENTY localizes to the Golgi complex (Ogawa-Ohnishi et al, 2013; Kassaw et al, 2017)

Summary

Introduction

Legumes have evolved the ability to make specialized root organs called nodules, in which nitrogen-fixing symbionts, rhizobial bacteria, reside. AtHPATs redundantly contribute to transferring an l-arabinosyl residue to the hydroxyl group of the hydroxyproline residues of several substrates, including extensin, AtCLE2, and Arabidopsis plant peptide containing sulfated tyrosine 1 (AtPSY1) (OgawaOhnishi et al, 2013; MacAlister et al, 2016). This discovery raised the possibility that LjPLENTY, MtRDN1, or PsNOD3 mediates the arabinosylation of their CLE peptides functioning in AON in the respective species. A recent study of the MtRDNs reported that, of the two CLE peptides, only MtCLE12 is required for a functional MtRDN1 to repress nodulation, suggesting that MtRDN1 post-translationally modifies MtCLE12 but not MtCLE13 (Kassaw et al, 2017)

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Results

Conclusion