AGL19 directly interacts with floral signal integrator AGL24 in flowering time control of Brassica juncea

Abstract

SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and AGAMOUS-LIKE 24 (AGL24) are pivotal flowering signal integrators, which respectively, belong to TM3/SOC1 and STMADS11 clades of MIKC-type MADS-box family. AGAMOUS-LIKE 19 (AGL19), one member of TM3/SOC1 clade family, acts as an activator of flowering time. Previous studies have suggested that AGL19 together with AGL24 and SOC1 coordinately regulate flowering time. However, it remains unknown how AGL19 interacts with SOC1 and AGL24 in Brassica juncea. Here, an AGL19-like (BjuAGL19) was cloned from B. juncea, which was expressed in roots, stems, leaves, buds and flowers. Furthermore, both yeast one-hybrid and Dual-Glo Luciferase assays confirmed that BjuAGL19 protein could not target the promoters of BjuSOC1 and BjuAGL24. Interestingly, based on yeast two-hybrid and pull-down assays, BjuAGL19 protein directly interacted with BjuAGL24 protein, instead of BjuSOC1 protein. It is speculated that BjuAGL19 can bind to BjuAGL24 to form protein complex of BjuAGL19-BjuAGL24 and thus regulates flowering time in B. juncea. The results are very helpful for further elucidating the molecular mechanism of BjuAGL19 in flowering time control.