Differential expression of poplar sucrose nonfermenting1-related protein kinase 2 genes in response to abiotic stress and abscisic acid

Knowledge on the responses of woody plants to abiotic stress can inform strategies to breed improved tree varieties and to manage tree species for environmental conservation and the production of lignocellulosic biomass. In this study, we examined the expression patterns of poplar (Populus trichocarpa) genes encoding members of the sucrose nonfermenting1-related protein kinase 2 (SnRK2) family, which are core components of the abiotic stress response. The P. trichocarpa genome contains twelve SnRK2 genes (PtSnRK2.1- PtSnRK2.12) that can be divided into three subclasses (I-III) based on the structures of their encoded kinase domains. We found that PtSnRK2s are differentially expressed in various organs. In MS medium-grown plants, all of the PtSnRK2 genes were significantly upregulated in response to abscisic acid (ABA) treatment, whereas osmotic and salt stress treatments induced only some (four and seven, respectively) of the PtSnRK2 genes. By contrast, soil-grown plants showed increased expression of most PtSnRK2 genes under drought and salt treatments, but not under ABA treatment. In soil-grown plants, drought stress induced SnRK2 subclass II genes in all tested organs (leaves, stems, and roots), whereas subclass III genes tended to be upregulated in leaves only. These results suggest that the PtSnRK2 genes are involved in abiotic stress responses, are at least partially activated by ABA, and show organ-specific responses.