Chimeric AGAMOUS repressor induces serrated petal phenotype in Torenia fournieri similar to that induced by cytokinin application

Abstract

The homeotic protein AGAMOUS (AG) terminates the floral meristem and promotes the development of stamens and carpels in Arabidopsis. Disruption of its function or expression of the chimeric AG repressor (AGSRDX) results in redundant petals, known as a double flower phenotype. To investigate whether this morphological change in Arabidopsis is applicable to ornamental flowers to increase their horticultural value, we introduced AGSRDX into torenia (Torenia fournieri Lind.) plants. Transgenic torenia plants expressing AGSRDX showed no redundancy in petal number, although they exhibited serration in petal margins, anthocyanin accumulation and morphological change in the stigma surface, and formation of extra vascular bundles in petals and styles. Anatomical observation of petals and styles revealed that these phenotypes are highly similar to those of forchlorfenuron (CPPU)-treated torenia plants especially in the derangement of vascular bundles. Phenotypes similar to AGSRDX transgenic torenia plants were also observed when the chimeric repressors for torenia C-function genes TfFAR or TfPLE1, homologs of Antirrhinum FARINELLI and PLENA respectively, were expressed. These results suggest that the morphological changes in AGSRDX transgenic torenia plants are induced by the disruption of C-function. These novel phenotypes might be caused by the modification of cytokinin-dependent regulation in vascular bundle formation and ectopic expression of the chimeric repressors in all whorls by the cauliflower mosaic virus (CaMV) 35S promoter.