Plants use information about daylight to align their flowering time with seasonal changes, increasing reproductive success. Long-day conditions promote flowering in model organism Arabidopsis thaliana. The gene FLOWERING LOCUS T (FT), which encodes florigen and promotes flowering, has been understood to show evening peak expression in long-day specific manner. The molecular mechanism responsible for FT regulation has been widely studied using 16-hour fluorescent white light, 8-hour dark, and constant 22°C as simplified long-day conditions. To expand our understandings on flowering regulation in nature, where multiple environmental signals synergistically regulate flowering, our lab analyzed FT expression in plants grown outdoors during Seattle’s summer solstice (15h59m daylight, 21.2°C high, average 1971 to 2000). In contrast to what has been reported under simplified long-day conditions, a morning and evening peak of FT expression was observed. Since 2014 we have succeeded in reconstructing natural double FT expression in growth chambers with 16-hour fluorescent light supplemented by far-red LED and temperature oscillation. My project addressed the effect of far-red light, as measured by the red to far-red light ratio (R:FR), on morning FT expression. Arabidopsis seedlings were grown for two weeks in chambers under constant temperature and 16-hour fluorescent light supplemented with variable strength of far-red light conditions, mimicking shade (0.25 to 0.75:1), natural sunlight (1:1) and fluorescent light (2:1). FT expression was analyzed using real-time quantitative reverse transcription PCR. As a result, higher FR ratio increased FT expression in wild-type. We are currently analyzing phytochrome mutants, lacking functional red and far-red light photoreceptors, to investigate how they are involved in FT regulation. FT function is widely conserved in angiosperms and identifying environmental inputs and the associated genes for flowering regulation in Arabidopsis under natural conditions can contribute to researching effects of climate change on flowering time in agriculturally relevant species.

Molecular studies of plants’ photoperiodic flowering have helped improve crops in agriculture and horticulture by modulating growth patterns in plants. A photoperiod is a seasonal change in day length of daytime that is consistent from year to year. Plants maximize their reproductive success by adjusting their flowering time according to photoperiodic information. To better understand the effect of photoperiods in plants, we used Arabidopsis thaliana as a model organism. Scientists worldwide study A.thaliana due to its genomic simplicity, its fast growth and its efficient transformation by using Agrobacterium tumefaciens. In A. thaliana, the transcription of the CONSTANS (CO) gene is key for the regulation of seasonal flowering. Under long-day conditions, both transcriptional and post-transcriptional CO regulation maximize the CO protein accumulation towards the end of day, which induces the expression of FLOWERING LOCUS T (FT) gene, which encodes florigen and causes the plants to flower. TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL NUCLEAR ANTIGEN FACTOR (TCP) binding site is closely located to cis-elements of CO regulators, which indicates that they might interact in the same complex. To study the functional interaction between TCP and known CO regulators, including GIGANTEA (GI) and FLOWERING bHLH (FBH), we first studied the protein-protein interaction using yeast two hybrid analysis. The yeast two hybrid analysis confirmed protein-protein interaction between TCP4-GI, TCP4-FBH, and FBH-GI. Then, to validate the protein-protein interaction suggested by the yeast two hybrid analysis we performed flowering time measurement experiments on multiple combinations of these mutants, in order to investigate the genetic relation among CO regulators.