Maize AKIN¦ Proteins Interact with P8 of Rice Black Streaked Dwarf Virus and Inhibit Viral Infection

Rice black streaked dwarf virus (RBSDV) is an important agent causing maize rough dwarf disease, whereas the host factors responding to RBSDV infection are poorly understood. To uncover the molecular interactions between RBSDV and maize, a yeast two-hybrid screen of a maize cDNA library was carried out using the viral P8 protein as a bait. ZmAKIN beta gamma-1 and ZmAKIN beta gamma-2 (beta gamma subunit of Arabidopsis SNF1 kinase homolog in maize) possessing high sequence similarities (encoded by two gene copies) were identified as interaction partners. Their interactions with P8 were confirmed in both Nicotiana benthamiana cells and maize protoplasts by bimolecular fluorescence complementation assay. The accumulation levels of ZmAKIN beta gamma mRNAs were upregulated at the stage of the viral symptoms beginning to appear and then downregulated. ZmAKIN beta gamma s are putative regulatory subunits of the SnRK1 complex, a core regulator for energy homeostasis. Knockdown of ZmAKIN beta gamma s in maize regulated the expression levels of the genes involved in sugar synthesis or degradation, and also the contents of both glucose and sucrose. Importantly, downregulation of ZmAKIN beta gamma s expressions facilitated the accumulation of RBSDV in maize. These results implicate a role of ZmAKIN beta gamma s in the regulation of primary carbohydrate metabolism, and in the defense against RBSDV infection.