Poster: Late and Moved Abstracts
Abs #
949: GIGANTEA acts in the phloem to promote photoperiodic flowering in Arabidopsis
Arabidopsis thaliana is a facultative long-day plant, flowering earlier under long days (LD) of 16hr light and later under short days of 10hrs of light. Mutations in GIGANTEA (GI) cause plants to be daylength insensitive, severely delaying flowering in LD conditions. These mutations reduce expression of downstream flowering-time genes such as CONSTANS (CO), whereas overexpression of GI causes early flowering by elevating the expression of CO. GI is a unique gene that encodes a nuclear localized protein of 1173aa and is highly conserved in the plant kingdom but not found in animals.
In addition to its effects on flowering, GI expression is regulated by the circadian clock and influences the circadian expression pattern of genes proposed to be involved in the circadian oscillator such as LHY and CCA1. It has also been suggested that GI is involved in phytochrome signalling as gi alleles cause an elongated hypocotyl in red light.
Photoperiod was previously shown to be perceived in the leaves and to promote flower development at the apex. As GI is widely expressed, we analysed in which tissues expression of GI is sufficient to promote flowering. Using various regional specific promoters to drive GI expression in the gi-3 mutant, we showed that specific misexpression of GI in the phloem results in early flowering of gi-3 in T1 and T2 lines, but expression in the meristem does not. Staining of GI::GUS plants also demonstrate that the gene is strongly expressed in the phloem. These data suggest that expression of GI in the phloem is sufficient to rescue the late flowering phenotype of the gi-3 mutant and that it may act in the phloem promote the synthesis of signals that are subsequently transmitted to the apex
