Function of LcAGL19 in the flowering regulation of Arabidopsis and Litchi chinensis

Litchi (Litchi chinensis Sonn.) is an important evergreen woody fruit tree. Appropriate low temperatures during autumn and winter are necessary for floral transition in litchi. However, global warming causes defective flowering, which seriously impedes the production of litchi. AGAMOUS-LIKE 19 (AGL19), a vernalization-related gene, had been found to control flowering time in Arabidopsis thaliana. However, its role in litchi remains unknown. In this study, we performed phylogenetic analysis. The results showed that LcAGL19 belonged to the SOC1/TM3-like protein family. Subcellular localization assay showed that LcAGL19 was localized on the nucleus. Ectopic expression of LcAGL19 in Arabidopsis thaliana resulted in early flowering, active inflorescence growth, and floral defects. Yeast two-hybrid assay and Firefly luciferase complementation imaging (LCI) assays showed that LcAGL19 might interact with MADS-box proteins to determine flowering time and floral organ identity. These results demonstrated that LcAGL19 might play important roles in floral transition, inflorescence and floral organ development in litchi. Our studies provided new insights into the regulation mechanisms of litchi flowering and offered meaningful references for AGL19 functional studies on other woody fruit trees. The functional study of LcAGL19 provided a genetic reference for litchi breeding.