Genome-wide characterization of the constitutively stressed (COST) family genes and their response to salt stress in poplar

In Arabidopsis, constitutively stressed 1 (COST1) negatively regulates drought tolerance by interacting with the key autophagy adaptor. However, the biological functions of COST family genes in other plants remain unknown. In this study, a total number of 11 PtCOST genes, distributed on 8 chromosomes, were identified in the poplar genome. Phylogenetic analysis indicated that they were classified into 4 groups, and have gone through 2 tandem and 7 segmental duplication events. The structures of PtCOST genes were highly conserved, with similar characteristics and an N -terminal DUF641 (domain of unknown function 641) domain. Cis-acting element analysis revealed that the promoter regions of PtCOST genes contained a variety of environmental stress, hormone and light response elements. Quantitative real -time PCR analysis displayed that PtCOSTs were constitutively expressed with overlapped but distinct expression patterns, and most of them were induced by salt stress. Further Arabidopsis cost1 mutant complementation experiments demonstrated that PtCOST3 was a functional homolog of COST1, and functioned as a negative regulator in response to salt stress. Our results provide fundamental information for further mechanism study of COST family genes in the growth, development and response to salinity stress in wooden plants.