Conservation and regulation of key photoperiod regulators in the Pooideae subfamily of grasses

Abstract

Plants have adapted to seasonal constraints of the temperate environment by exploiting annual fluctuations in day length. Well timed flowering is essential to maximize reproductive output in temperate regions with short growing seasons. Many temperate plants time their flowering response with lengthening photoperiods to anticipate the favorable growing seasons in late spring and early summer. Photoperiodic regulators are the keys that unlock the flowering response mechanism. The key photoperiodic regulators being investigated in thesis are the genes CONSTANS (CO), PHOTOPERIOD 1 (PPD1) and PHYTOCHROME C (PHYC). As a study system, I will use the Pooideae subfamily of grasses, which dominate northern temperate and arctic environments. This largely long-day flowering subfamily evolved from a short-day flowering ancestor. Phylogenetic analysis of the CO1 and CO2 paralogs revealed a duplication at the base of the Pooideae, however while CO2 was well represented in the core Pooideae species only a few basal species possessed the CO2 paralog. This may indicate that CO2 evolved a function in flowering relatively late in the evolutionary history of Pooideae. PPD1 was highly expressed in long days in comparison with short days in the basal Pooideae Piptatherum milaceum. This is similar with expression patterns in long day flowering Pooideae model species. This suggests that this gene evolved to be a key photoperiodic regulator in longday flowering, implying that the evolution of long day flowering in the Pooideae subfamily may be centered on this gene.