The AGL6-like Gene CpAGL6, a Potential Regulator of Floral Time and Organ Identity in Wintersweet (Chimonanthus praecox)

Wintersweet (Chimonanthus praecox), a deciduous aromatic shrub endemic to China, has high ornamental value for developing beautiful flowers with strong fragrance. The transition from the vegetative to the reproductive phase in wintersweet takes 4-5 years. The molecular mechanism regulating flower development in this basal angiosperm is largely unknown. Here we characterized the molecular features and expression patterns of the C. praecox AGL6-like gene CpAGL6 and investigated its potential role in regulating floral time and organ development via ectopic expression in Arabidopsis thaliana. The expression of CpAGL6 is highly tissue-specific, with the highest level in the middle tepals, moderate levels in inner tepals and carpels, and weak levels in stamen and young leaf tissues. Its dynamic expression in the flower is coincident with tepal opening. Ectopic expression of CpAGL6 in Arabidopsis retarded the vegetative growth and led to precocious flowering, mainly correlated with the inhibition of the floral repressor FLC and promotion of the floral promoters AP1 and FT. Although no ectopic floral organs have been observed, transgenic plants exhibited abnormal stamen and carpel development in later-developing flowers, with fertility reduced to varying degrees. These results suggest that CpAGL6, the AGL6-like gene from the basal angiosperm C. praecox, is a potential E-function regulator involved in specifying floral time and organ identity, functionally homologous to those AGL6-like genes from higher eudicots and monocots.