Metallothionein1A Regulates Rhizobial Infection and Nodulation in Phaseolus vulgaris.

Citlali Fonseca-García,Carmen Quinto,Jorge Solis-Miranda,Claudia Marina López-García,Elisabeth Armada,Rocío Pérez-Aguilar,Ronal Pacheco,Noreide Nava

doi:10.3390/ijms23031491

Abstract

Metallothioneins (MTs) constitute a heterogeneous family of ubiquitous metal ion-binding proteins. In plants, MTs participate in the regulation of cell growth and proliferation, protection against heavy metal stress, oxidative stress responses, and responses to pathogen attack. Despite their wide variety of functions, the role of MTs in symbiotic associations, specifically nodule-fabacean symbiosis, is poorly understood. Here, we analyzed the role of the PvMT1A gene in Phaseolus vulgaris-Rhizobium tropici symbiosis using bioinformatics and reverse genetics approaches. Using in silico analysis, we identified six genes encoding MTs in P. vulgaris, which were clustered into three of the four classes described in plants. PvMT1A transcript levels were significantly higher in roots inoculated with R. tropici at 7 and 30 days post inoculation (dpi) than in non-inoculated roots. Functional analysis showed that downregulating PvMT1A by RNA interference (RNAi) reduced the number of infection events at 7 and 10 dpi and the number of nodules at 14 and 21 dpi. In addition, nodule development was negatively affected in PvMT1A:RNAi transgenic roots, and these nodules displayed a reduced nitrogen fixation rate at 21 dpi. These results strongly suggest that PvMT1A plays an important role in the infection process and nodule development in P. vulgaris during rhizobial symbiosis.

Highlights

Published: 27 January 2022 Publisher’sNote: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland
These findings suggest that, all four MT clades are distributed throughout the angiosperms and evolved before the divergence of monocots and dicots, gene structure and close phylogenetic relationships are conserved within each group
Our findings provide compelling experimental evidence highlighting the role of MTs in rhizobial infection and in nodule development during the mutualistic interaction between common bean and R. tropici

Summary

Introduction

Published: 27 January 2022 Publisher’sNote: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland. Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The fabacean common bean (Phaseolus vulgaris L.) can establish a symbiotic relationship with soil bacteria known as rhizobia This symbiotic interaction between fabaceans and rhizobia, hereafter referred to as fabacean-rhizobia symbiosis, begins with an exchange of chemical signals, in which the roots exude flavonoids that induce the synthesis and secretion of lipo-chitooligosaccharides, i.e., nodulation factors (NFs), by the rhizobia [1]. Rhizobial infection normally occurs through root hairs [4], which tips curl in the presence of the rhizobia, forming “infection pockets” [5]. This process is followed by invagination of the plasma membrane, which develops tubular structures called infection threads (ITs). ITs function as tunnels that guide the rhizobia toward the cortical cells, where the nodule primordia form [4,6]

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