Editorial: Food Legume Diversity and Legume Research Policies

Genome-wide identification of the TGA genes in common bean (Phaseolus vulgaris) and revealing their functions in response to Fusarium oxysporum f. sp. phaseoli infection

Fusarium wilt, which affects common bean all across the world, is caused by Fusarium oxysporum f. sp. Phaseoli (Fop). It is necessary to have functional genes in response to Fop infection because they might be used to manage disease. As a crucial regulator, TGA-binding transcription factor (TGA) is engaged in the defense mechanism of plants against pathogens. The role of TGA regulators in common bean in response to Fop infection, however, has not been documented. Hence, we performed genome-wide identified and characterized eight TGA genes in common bean. In this study, eight PvTGA genes were distributed on six chromosomes and classified into four subgroups. The PvTGA genes have the same conserved bZIP and DOG1 domains, but there are specific sequence structures in different PvTGAs. Phylogenetic and synteny analysis explained that PvTGA gene has a close genetic relationship with legume TGAs and that PvTGA03 and PvTGA05 may play an important role in evolution. Transcriptome data explained that expression levels of PvTGA genes showed diversity in different tissues. After Fop inoculation, the expression levels of PvTGA03 and PvTGA07 were significantly different between resistant and susceptible genotypes. Under SA treatment, the expression levels of PvTGA03, PvTGA04, PvTGA06, PvTGA07 and PvTGA08 were significantly different. These results imply that PvTGA03 and PvTGA07 play key roles in SA-mediated resistance to Fusarium wilt. Together, these findings advance knowledge of the PvTGA gene family in common bean and will help future studies aimed at reducing Fusarium wilt.

A methyl esterase 1 (PvMES1) promotes the salicylic acid pathway and enhances Fusarium wilt resistance in common beans

Methyl esterase (MES), PvMES1, contributes to the defense response toward Fusarium wilt in common beans by regulating the salicylic acid (SA) mediated signaling pathway from phenylpropanoid synthesis and sugar metabolism as well as others. Common bean (Phaseolus vulgaris L.) is an important food legume. Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli is one of the most serious soil-borne diseases of common bean found throughout the world and affects the yield and quality of the crop. Few sources of Fusarium wilt resistance exist in legumes and most are of quantitative inheritance. In this study, we have identified a methyl esterase (MES), PvMES1, that contributes to plant defense response by regulating the salicylic acid (SA) mediated signaling pathway in response to Fusarium wilt in common beans. The result showed the role of PvMES1 in regulating SA levels in common bean and thus the SA signaling pathway and defense response mechanism in the plant. Overexpression of the PvMES1 gene enhanced Fusarium wilt resistance; while silencing of the gene caused susceptibility to the diseases. RNA-seq analysis with these transiently modified plants showed that genes related to SA level changes included the following gene ontologies: (a) phenylpropanoid synthesis; (b) sugar metabolism; and (c) interaction between host and pathogen as well as others. These key signal elements activated the defense response pathway in common bean to Fusarium wilt. Collectively, our findings indicate that PvMES1 plays a pivotal role in regulating SA biosynthesis and signaling, and increasing Fusarium wilt resistance in common bean, thus providing novel insight into the practical applications of both SA and MES genes and pathways they contribute to for developing elite crop varieties with enhanced broad-spectrum resistance to this critical disease.

Resequencing of 683 common bean genotypes identifies yield component trait associations across a north-south cline

We conducted a large-scale genome-wide association study evaluation of 683 common bean accessions, including landraces and breeding lines, grown over 3 years and in four environments across China, ranging in latitude from 18.23° to 45.75° N, with different planting dates and abiotic or biotic stresses. A total of 505 loci were associated with yield components, of which seed size, flowering time and harvest maturity traits were stable across years and environments. Some loci aligned with candidate genes controlling these traits. Yield components were observed to have strong associations with a gene-rich region on the long arm of chromosome 1. Manipulation of seed size, through selection of seed length versus seed width and height, was deemed possible, providing a genome-based means to select for important yield components. This study shows that evaluation of large germplasm collections across north-south geographic clines is useful in the detection of marker associations that determine grain yield in pulses.