Transcriptome and Proteins Analysis Reveals the Gene Regulatory Processes Mediated by LaAP2L1 , an AP2/ERF Transcription Factor, Functioning in Fast-Growing Heterosis in Larix kaempferi

Larix is an important commercial tree species and possesses huge value in ecological protection. Heterosis is a common genetic phenomenon in Larix , and it has been widely used to breed new varieties with fast-growing trait. However, compared with the large-scale planting of F 1 hybrids in the afforestation of Larix , the molecular basis and regulatory mechanism of heterosis remain ambiguous. In a previous study, LaAP2L1 , an APETALA2/ethylene responsive element binding factor (AP2/ERF) transcription factor (TFs), was cloned from L. kaempferi and confirmed to play a crucial role in the formation of fast-growing heterotic trait of F 1 hybrids. However, the regulatory mechanism of LaAP2L1 remains unclear. In the present study, the proteins that interact with LaAP2L1 were identified by screening a yeast two-hybrid library. A total of 109 proteins were identified to interact with LaAP2L1, among which NdhL, YUC6, TOPP1, AMSH2, SPDS2, EIP9, and DMR6 showed strong interactions with LaAP2L1. In addition, 4831 differentially expressed genes (DEGs) were identified between the LaAP2L1 -overexpressing transgenic lines and vector controls. These DEGs displayed significant enrichment in the regulatory processes associated with the synthesis and establishment of cell components, such as cell wall, cytoskeleton, and ribosome; gibberellin metabolism; cell cycle phase transition; carbohydrate metabolism; and circadian rhythm regulation. These results suggested that LaAP2L1 functions in the formation of heterosis, mainly by regulating these growth and development processes via interacting with proteins, such as NdhL, YUC6, TOPP1, AMSH2, SPDS2, EIP9, and DMR6. The findings provide new insights into the regulation of LaAP2L1 in the formation of fast-growing heterotic trait in Larix .