CRYPTOCHROME2 in Vascular Bundles Regulates Flowering in Arabidopsis

Abstract

Plants make full use of light signals to determine the timing of flowering. In Arabidopsis thaliana, a blue/UV-A photoreceptor, CRYPTOCHROME 2 (cry2), and a red/far-red photoreceptor, PHYTOCHROME B (phyB), are two major photoreceptors that control flowering. The light stimuli for the regulation of flowering are perceived by leaves. We have recently shown that phyB expression in mesophyll but not in vascular bundles suppresses the expression of a key flowering regulator, FLOWERING LOCUS T (FT), in vascular bundles. In this study, we asked where in the leaf cry2 perceives light stimuli to regulate flowering. To answer this question, we established transgenic Arabidopsis lines in which the cry2-green fluorescent protein (GFP) fusion was expressed under the control of organ/tissue-specific promoters in a cry2-deficient mutant background. Analysis of these lines revealed that expression of cry2-GFP in vascular bundles, but not in epidermis or mesophyll, rescued the late flowering phenotype. We further confirmed that cry2-GFP expressed in vascular bundles increased FT expression only in vascular bundles. Hence, in striking contrast with phyB, cry2 most likely regulates FT expression in a cell-autonomous manner.

PHYTOCHROME-DEPENDENT LATE-FLOWERING accelerates flowering through physical interactions with phytochrome B and CONSTANS

“…Consistent with this view, type II phytochromes (mainly phyB) are shown to regulate CO protein stability (13,17), although phyB is also known to regulate CO mRNA levels as well (8,9). As we previously reported, photoreceptors, including phyB, have tissue specificity for flowering regulation (38)(39)(40). Dual regulation by one factor is also seen in a blue-light receptor FKF1, which regulates both CO mRNA and CO protein stability by different mechanisms (12,14).…”

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

“…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). Therefore, a role of FT in the cry-mediated effects on stomatal opening cannot be ruled out.…”

“…1). Furthermore, while cry2 is the main cry in terms of induction of FT expression (Endo et al, 2007), cry1 and cry2 redundantly enhance stomatal conductance.…”

Tissue- and isoform-specific phytochrome regulation of light-dependent anthocyanin accumulation in Arabidopsis thaliana

“…Although total levels of pools of phytochromes and cryptochromes contribute to the photoregulation of distinct photoreceptor-dependent responses. [37][38][39][40] Mesophyll-localized phytochromes are associated with the photoperiodic control of flowering, 38 the photoregulation of hypocotyl elongation, 39,40 and light-dependent pigment accumulation. 40 Cryptochrome 2 in vascular bundles regulates flowering.…”