Differential floral development and gene expression in grapevines during long and short photoperiods suggests a role for floral genes in dormancy transitioning.

Daylength is an important environmental cue for synchronizing growth, flowering, and dormancy with seasonality. As many floral development genes are photoperiod regulated, it has been suggested that they could have a regulatory role in bud endodormancy. Therefore, the influence of photoperiod was studied on inflorescence primordia differentiation and floral pathway related gene expression during the development of overwintering buds in Vitis riparia and V. spp. 'Seyval'. Photoperiod treatments were imposed 35 days after budbreak, and histological and transcriptomic analyses were conducted during the subsequent 42 days of bud development. Long day (LD, 15 h) and short day (SD, 13 h) buds were floral competent by 21 days of photoperiod treatment (56 days after budbreak); however, the floral meristem developed faster in LD than in SD buds. Analysis of 132 floral pathway related genes represented on the Affymetrix Grape Genome array indicated 60 were significantly differentially expressed between photoperiod treatments. Genes predominantly related to floral transition or floral meristem development were identified by their association with distinct grape floral meristem development and an expression pattern in LD consistent with their previously identified roles in flowering literature. Genes with a potential dual role in floral development and dormancy transitioning were identified using photoperiod induced differences in floral development between LD and SD buds and uncharacteristic gene expression trends in relation to floral development. Candidate genes with the potential to play a dual role in SD dormancy induction include circadian rhythm or flowering transition related genes: AP2, BT1, COL-13, EIN3, ELF4, DDTR, GAI and HY5.