Characterization of Plant Defensin (PDF) Genes in Banana (Musa acuminata) Reveals the Antifungal Ability of MaPDF2.2 to Fusarium Wilt Pathogens

Plant defensin (PDF/DEF), an important pathogenesis-related protein which widely exists in plants, displays broad-spectrum antifungal activities. To date, however, reports on the banana PDFs are very limited. In this study, we identified, cloned, and characterized the five Class I PDFs (MaPDF2.1~MaPDF2.5) in banana (Musa acuminata). Further, their expression in root, corm, leaf, and fruit were studied. MaPDFs exhibited quite different expression patterns in different organs, with MaPDF2.2 as the only member expressing in all the tested organs, and its expression levels in all organs were the highest among all MaPDFs. The MaPDF2.2 expression could be significantly upregulated by both low- and high-temperature stresses but significantly downregulated by the inoculations of plant growth promoting endophytic fungus Serendipita indica and banana Fusarium wilt (FW) pathogen Fusarium oxysporum f. sp. cubense (Foc) Tropical race 4 (FocTR4). Moreover, the S. indica pre-colonization could significantly alleviate the suppression of FocTR4 on MaPDF2.2, suggesting that this MaPDF might contribute greatly to the S. indica-enhanced FW resistance. By using tobacco leaf transient overexpression, the function of MaPDF2.2 was investigated. Its overexpression significantly inhibited the infection of Foc race 1 (Foc1) and FocTR4 in tobacco leaves. Furthermore, in vitro antifungal ability assays revealed that the recombinant His-MaPDF2.2 protein could significantly inhibit the growth of Foc1 and FocTR4, as well as the pigment accumulation of Foc1. Our study revealed the sequence and expression characteristics of banana PDFs and demonstrated the antifungal ability of MaPDF2.2 to FW pathogens.