FLOWERING LOCUS T Regulates Stomatal Opening

Abstract

Stomatal pores surrounded by a pair of guard cells in the plant epidermis control gas exchange for photosynthesis in response to light, CO(2), and phytohormone abscisic acid. Phototropins (phot1 and phot2) are plant blue-light receptor kinases and mediate stomatal opening via activation of the plasma membrane H(+)-ATPase. However, the signaling mechanism from phototropins to the H(+)-ATPase has yet to be determined. Here, we show that FLOWERING LOCUS T (FT) is expressed in guard cells and regulates stomatal opening. We isolated an scs (suppressor of closed-stomata phenotype in phot1 phot2) 1-1 mutant of Arabidopsis thaliana and showed that scs1-1 carries a novel null early flowering 3 (elf3) allele in a phot1 phot2 background. scs1-1 (elf3 phot1 phot2 triple mutant) had an open-stomata phenotype with high H(+)-ATPase activity and showed increased levels of FT mRNA in guard cells. Transgenic plants overexpressing FT in guard cells showed open stomata, whereas a loss-of-function FT allele, ft-1, exhibited closed stomata and failed to activate the H(+)-ATPase in response to blue light. Our results define a new cell-autonomous role for FT and demonstrate that the flowering time genes ELF3 and FT are involved in the regulation of H(+)-ATPase by blue light in guard cells.

Overexpression of plasma membrane H + -ATPase in guard cells promotes light-induced stomatal opening and enhances plant growth

“…S7). In addition, the stomata of FT-transgenic plants (GC1::FT-GFP), which have a normal ABA response, were constantly open with a wide aperture under both light and dark conditions (22). However, the growth of FT-transgenic plants was comparable to that of WT plants (Table 2).…”

“…To produce transgenic plants showing enhanced stomatal opening in response to light, we attempted to express three key components of stomatal opening: PHOTOTROPIN 2 (PHOT2), an isoform of the blue light receptor phototropin (13); ARABIDOPSIS H + -ATPASE 2 (AHA2), a typical isoform of the plasma membrane H + -ATPase (24); and POTASSIUM CHANNEL IN ARABIDOPSIS THALIANA 1 (KAT1) and ARABIDOPSIS K + TRANSPORTER 1 (AKT1), isoforms of plasma membrane K + in channels (19,20,(25)(26)(27). We used the strong guard cell promoter GC1 (22,23) because these proteins function exclusively within guard cells. Immunohistochemical and Western blotting analyses demonstrated that the levels of AHA2 expressed under the control of the GC1 promoter (GC1::AHA2) in guard cells of AHA2-transgenic plants were ∼1.5-fold higher than in wild-type (WT) guard cells ( Fig.…”

“…S7 B and C). We also examined FT-transgenic plants (GC1::FT-GFP) because FT is a positive regulator of stomatal opening (22). Stomata of FT-transgenic plants were constantly open with a larger aperture than the stomata of WT plants under light and dark conditions but closed in response to ABA (22).…”

“…Thus, these three components (phototropins, plasma membrane H + -ATPase, and K + in channels) have important roles in blue light-induced stomatal opening. In addition to these components, FLOWERING LOCUS T (FT) is suggested to be a positive regulator for stomatal opening via its effect on the activation status of the plasma membrane H + -ATPase (22).…”

Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight

“…The expression of FLOWERING LOCUS T (FT) in occlusive cells has recently been shown to be important for the induction of stomatal opening by blue light (Kinoshita et al, 2011). In Arabidopsis plants exposed to long days, cry (mainly cry2) promotes the expression of FT in vascular tissues (Endo et al, 2007;Kobayashi and Weigel, 2007), and the FT protein then migrates to the apex to induce the transition to flowering (Corbesier et al, 2007).…”