Seasonal changes in the expression pattern of flowering-related genes in evergreen azalea ‘Oomurasaki’ ( Rhododendron × pulchrum)

Abstract

To investigate seasonal changes in transcript levels of flowering-related genes corresponding to shoot condition, the endogenous expression patterns of FLOWERING LOCUS T ( FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC1), LEAFY ( LFY), TERMINAL FLOWER 1 ( TFL1), and CENTRORADIALIS ( CEN) homologs were investigated in evergreen azalea ‘Oomurasaki’. In this plant, in which the floral transition is triggered by the about 25 °C and shortening days of summer under natural conditions, the mRNA levels of the FT, SOC1, and LFY homologs ( RpFT, RpSOC1, and RpLFY) increased in August corresponding to the period of flower bud formation, and the mRNA levels of TFL1 and CEN homologs ( RpTFL1 and RpCEN) increased during July before flower bud formation. RpTFL1 showed low transcript levels during the period of flower bud formation and development, but RpCEN showed a different expression pattern from RpTFL1. The expression of RpCEN, RpSOC1, and RpLFY peaked again during January corresponding to the period of flower bud dormancy. During blooming in May, the expression levels of all the investigated genes were low. In the period of flower bud formation, RpFT expression started to increase, and the expression of RpSOC1 peaked in mid-July. These results suggest that the shoot apical meristem (SAM) starts to transition from vegetative to reproductive growth in mid-July. Thus, changes in the transcription of RpFT, RpSOC1, and RpLFY were found to correlate positively with seasonal flowering in the shoot apex of ‘Oomurasaki’, whereas changes in RpTFL1 and RpCEN transcription correlated negatively with seasonal flowering.