Control of the Rhizobia Nitrogen-Fixing Symbiosis by Common Bean MADS-Domain/AGL Transcription Factors.

Plants MADS-domain/AGL proteins constitute a large transcription factor (TF) family that controls the development of almost every plant organ. We performed a phylogeny of (. 500) MADS-domain proteins from Arabidopsis and four legume species. We identified clades with Arabidopsis MADS-domain proteins known to participate in root development that grouped legume MADS-proteins with similar high expression in roots and nodules. In this work, we analyzed the role of AGL transcription factors in the common bean () - N-fixing symbiosis. Sixteen genes (), out of 93 family members, are expressed - at different levels - in roots and nodules. From there, we selected the gene denominated -like for overexpression or silencing in composite plants, with transgenic roots and nodules, that were used for phenotypic analysis upon inoculation with . Because of sequence identity in the DNA sequence used for RNAi-like construct, roots, and nodules expressing this construct -referred to as RNAi_- showed lower expression of other five genes highly expressed in roots/nodules. Contrasting with -like overexpressing plants, rhizobia-inoculated plants expressing the RNAi_ silencing construct presented affection in the generation and growth of transgenic roots from composite plants, both under non-inoculated or rhizobia-inoculated condition. Furthermore, the rhizobia-inoculated plants showed decreased rhizobial infection concomitant with the lower expression level of early symbiotic genes and increased number of small, ineffective nodules that indicate an alteration in the autoregulation of the nodulation symbiotic process. We propose that the positive effects of PvAGL TF in the rhizobia symbiotic processes result from its potential interplay with NIN, the master symbiotic TF regulator, that showed a CArG-box consensus DNA sequence recognized for DNA binding of AGL TF and presented an increased or decreased expression level in roots from non-inoculated plants transformed with OE_ or RNAi_ construct, respectively. Our work contributes to defining novel transcriptional regulators for the common bean - rhizobia N-fixing symbiosis, a relevant process for sustainable agriculture.