Identification and functional characteristics of key regulatory genes in Populus alba in response to cold stress

Forest crops are particularly susceptible to cold stress after dormancy release. Newly emerged shoots are especially vulnerable, and shoot mortality can cause serious loss of biomass production. Revealing the molecular mechanisms of cold stress responses in forest trees is therefore crucial. Populus alba is a frost-resistant tree species distributed worldwide. In this study, we characterized the transcriptome of P. alba in response to cold stress and observed that a large number of genes were up-regulated in both root and leaf tissues. Through Mfuzz clustering and phylogenetic analysis, four ethylene-responsive factor (ERF) genes (PoalbERF73/80/86/124) were identified as cold-responsive genes. These four genes belong to group IX of the ERF family, and exhibited distinct tissue-specific expression patterns. We generated overexpression and knockout mutants of these four ERF genes in P. alba. Comprehensive morphological and physiological characteristics of the transgenic and mutant lines indicated that these ERF genes are involved in the cold stress response. Our results provide further insights into the genetic basis of cold tolerance in trees.