DELLA gene expression may be involved in chasmogamous–cleistogamous flower development and regulate the expression of B-class floral homeotic genes in Viola philippica

Viola philippica forms chasmogamous (CH) and cleistogamous (CL) flowers under different photoperiods on the same plant: short-day conditions induce CH flowers, while photoperiod extension induces CL flower formation. The content of active gibberellins (GAs) in CL flowers under long daylight conditions is greater than that in CH flowers under short daylight conditions. This study investigated the relationships between the expression of DELLA genes in GA signaling pathways and CH–CL flower development. The cDNA sequences of three DELLA genes were isolated and designated VphGAI , VphRGL2 , and VphRGL3 . The expression of VphGAI , VphRGL2 , and VphRGL3 was higher in CH flowers under a 10 h/14 h photoperiod than in intermediate CL flowers and CL flowers under 12 h/12 h and 16 h/8 h photoperiods. VphGAI , VphRGL2 , and VphRGL3 were significantly downregulated after treatment with lower concentrations of exogenous GA 3 under the three photoperiods. In addition, VphGAI could bind to the B-class floral homeotic gene promoters and inhibit their transcription. NbGAI -silenced Nicotiana benthamiana plants produced using VphGAI as a probe displayed earlier flowering; longer stamen filaments; larger leaves, flowers, and anthers; and the higher expression of B-class floral homeotic genes than the control group. These results suggest that DELLA gene expression may be related to CH–CL flower development and participate in CL flower filament development in V. philippica . Our work provides a theoretical basis for the molecular mechanisms of the dimorphic flower development in Viola .