| Summary: | The regulation of abscission has a significant impact on fruit yield and quality. Thus, understanding the mechanisms underlying abscission, particularly identifying key genes, is critical for improving fruit crop breeding and cultivation practices. Here, to explore the key genes involved in litchi fruitlet abscission, the two closest homologs of AGAMOUS-like 15/18 (LcAGL15 and LcAGL18) were identified. During the litchi fruitlet abscission process, <i>LcAGL15</i> expression was reduced, whereas <i>LcAGL18</i> expression was increased at the abscission zone. The abscission of floral organs was unaffected by ectopic expression of <i>LcAGL15</i> in <i>Arabidopsis</i>. Moreover, high expression of <i>LcAGL18</i> significantly delayed the abscission process of floral organs, particularly the sepals. Overexpression of <i>LcAGL18</i> in <i>Arabidopsis</i> consistently repressed the expression of abscission-related genes, including HAESA (HAE) and HAESA-LIKE2 (HSL2), and cell wall remodeling genes at the abscission zone. Furthermore, LcAGL18 was localized in the nucleus and acted as a transcriptional inhibitor. Collectively, these results suggest that AGL18 homologs have conserved functions in <i>Arabidopsis</i> and litchi, and that LcAGL18 might function as a key regulator in litchi fruitlet abscission.
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