Genome-Wide Analysis of ABF Gene Family in Lettuce (Lactuca sativa L.) Reveals the Negative Roles of LsABF1 in Thermally Induced Bolting

As one of the most significant leafy vegetables, the occurrence of early bolting due to high temperatures during summer has emerged as a significant challenge in the annual cultivation production of leaf lettuce, demanding urgent resolution. ABF transcription factors, also known as ABA-responsive element binding factors, are a class of basic leucine zipper (bZIP) proteins that specifically recognize ABREs and play a critical role in the ABA signaling pathway. In this study, we identified 8 members of the ABF gene family in leaf lettuce. A phylogenetic analysis was conducted on the ABF members of leaf lettuce, which resulted in the clustering of these members into three groups: A, B, and C. By performing a multiple sequence alignment analysis, it was observed that all LsABFs contain a highly conserved domain, RMIKNRESAARSRARKQAY (Bzip_plant_BZIP46). The result of tandem duplication events analysis in the ABF genes showed that there were two pairs of tandem duplication genes: LsABF2-LsABF1and LsABF3-LsABF1. A total of 1242 cis-acting elements were identified, and 323 cis-acting elements were screened out. In phosphorylation site analysis, a total of 304 phosphorylation sites were predicted. All LsABFs members had similar expression patterns, and their expression on the 8th day was significantly higher than the control, suggesting their involvement in the bolting process. Silencing LsABF1 has a positive effect on bolting in leaf lettuce, indicating that LsABF1 is a potential regulator of lettuce bolting. This study provides a theoretical basis for a better understanding of the molecular mechanisms underlying the ABF genes in high-temperature-induced bolting.