The Functional Characterization of MaGS2 and Its Role as a Negative Regulator of Ciboria shiraiana

Glutamine synthetase (GS) is a key enzyme involved in nitrogen metabolism. GS can be divided into cytosolic and plastidic subtypes and has been reported to respond to various biotic and abiotic stresses. However, little research has been reported on the function of GS in mulberry. In this study, the full length of MaGS2 was cloned, resulting in 1302 bp encoding 433 amino acid residues. MaGS2 carried the typical GS2 motifs and clustered with plastidic-subtype GSs in the phylogenetic analysis. MaGS2 localized in chloroplasts, demonstrating that MaGS2 is a plastidic GS. The expression profile showed that MaGS2 is highly expressed in sclerotiniose pathogen-infected fruit and sclerotiniose-resistant fruit, demonstrating that MaGS2 is associated with the response to sclerotiniose in mulberry. Furthermore, the overexpression of MaGS2 in tobacco decreased the resistance against Ciboria shiraiana, and the knockdown of MaGS2 in mulberry by VIGS increased the resistance against C. shiraiana, demonstrating the role of MaGS2 as a negative regulator of mulberry resistance to C. shiraiana infection.