Identification of ABCG gene family in Larix kaempferi and preliminary exploration on its drought resistance function

Objective To systematically identify and characterize the ATP-binding cassette G subfamily (ABCG) genes in Larix kaempferi and evaluate their potential roles in drought stress response.

Method A genome-wide survey of ABCG gene family in L. kaempferi was conducted using bioinformatics approaches, followed by analyses of phylogenetic relationships, conserved motifs, promoter cis-acting elements, and molecular docking. In addition, the expression patterns of these genes in different tissues under drought treatment were examined by real-time quantitative PCR, and a candidate gene was preliminarily evaluated using a yeast heterologous expression system.

Result (1) A total of 20 LkABCG genes were identified and distributed across 13 scaffolds. (2) Phylogenetic analysis classified the LkABCG family into three major groups, with no members assigned to Group Ic. Combined analyses of conserved motifs and Ka/Ks values indicated that the family was generally evolutionarily conserved, although divergence among subgroups was evident. (3) Molecular docking suggested that different LkABCG proteins may have distinct binding preferences for phytohormones, phenylpropanoid-related metabolites, and lipid- or cuticular barrier-related compounds. (4) Numerous hormone- and stress-responsive cis-acting elements were identified in the promoter regions of LkABCG genes. Expression analysis revealed differential expression among tissues, and several genes responded markedly to drought treatment. (5) Under 6% PEG4000-simulated drought stress, yeast expressing LkABCG36 showed better growth than control, suggesting that it may be involved in drought stress response.

Conclusion The LkABCG gene family is generally conserved in L. kaempferi, whereas functional diversification may have occurred among different groups. Evidence from sequence features, promoter composition, expression profiles, docking predictions, and yeast assays suggests that some LkABCG genes may participate in drought-related stress responses. These findings provide a basis for identifying drought-responsive candidate genes and for further functional validation in L. kaempferi.