Expression and Functional Analysis of a Novel Group of Legume-specific WRKY and Exo70 Protein Variants from Soybean

Legumes fix atmospheric nitrogen through symbiosis with microorganisms and contain special traits in nitrogen assimilation and associated processes. Recently, we have reported a novel WRKY-related protein (GmWRP1) and a new clade of Exo70 proteins (GmExo70J) from soybean with homologs found only in legumes. GmWRP1 and some of the GmExo70J proteins are localized to Golgi apparatus through a novel N-terminal transmembrane domain. Here, we report further analysis of expression and functions of the novel GmWRP1 and GmExo70J genes. Promoter-GUS analysis in Arabidopsis revealed distinct tissue-specific expression patterns of the GmExo70J genes not only in vegetative but also in reproductive organs including mature tissues, where expression of previously characterized Exo70 genes is usually absent. Furthermore, expression of some GmExo70J genes including GmExo70J1, GmExo70J6 and GmExo70J7 increases greatly in floral organ-supporting receptacles during the development and maturation of siliques, indicating a possible role in seed development. More importantly, suppression of GmWRP1, GmExo70J7, GmExo70J8 and GmExo70J9 expression in soybean using virus- or artificial microRNA-mediated gene silencing resulted in accelerated leaf senescence and reduced nodule formation. These results strongly suggest that legume-specific GmWRP1 and GmExo70J proteins play important roles not only in legume symbiosis but also in other processes critical for legume growth and development.