Mutations in the gene for the red/far-red light receptor phytochrome B alter cell elongation and physiological responses throughout Arabidopsis development.

Abstract

Phytochromes are a family of plant photoreceptors that mediate physiological and developmental responses to changes in red and far-red light conditions. In Arabidopsis, there are genes for at least five phytochrome proteins. These photoreceptors control such responses as germination, stem elongation, flowering, gene expression, and chloroplast and leaf development. However, it is not known which red light responses are controlled by which phytochrome species, or whether the different phytochromes have overlapping functions. We report here that previously described hy3 mutants have mutations in the gene coding for phytochrome B (PhyB). These are the first mutations shown to lie in a plant photoreceptor gene. A number of tissues are abnormally elongated in the hyd(phyt3) mutants, including hypocotyls, stems, petioles, and root hairs. In addition, the mutants flower earlier than the wild type, and they accumulate less chlorophyll.PhyB thus controls Arabidopsis development at numerous stages and in multiple tissues.

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

“…Therefore, it is proposed that phyB plays a dominant role in the shadeavoidance reaction in cucumber. Similar conclusions have been drawn from the study of the following mutants: Arabidopsis thaliana phyB (hy3, Nagatani et al, 1991;Somers et al, 1991), which is mutated in the P H Y B gene itself (Reed et al, 1993); Brussica rapa ein (Devlin et al, 1992); lv of pea (Nagatani et al, 1990; J.L. Weller, personal communication); and transgenic Arabidopsis overexpressing PHYA or PHYB (McCormac et al, 1993).…”

NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day in Arabidopsis

“…Previously, flowering-time mutants that are affected only under SD conditions have been reported. For example, phyB, dnf, spa1 and cop1 flower early, whereas vil1, vil2 and a gain-of-function mutation in IAA7/AXR2 (axr2-1) flower late specifically under SD conditions (Ishikawa et al, 2006;Kim and Sung, 2010;Laubinger et al, 2006;Mai et al, 2011;McNellis et al, 1994;Morris et al, 2010;Reed et al, 1993;Sung et al, 2006). However, vil1, vil2 and axr2-1 mutants display quantitative differences in flowering time compared with the wt and still flower under SD conditions (Kim and Sung, 2010;Mai et al, 2011;Sung et al, 2006).…”

Two Small Spatially Distinct Regions of Phytochrome B Are Required for Efficient Signaling Rates.

“…Contrasting photosensory functions of the phyA and phyB holoproteins have been defined through analysis of responses to constitutive overexpression of Quail, 1989, 1991;Kay et al, 1989;Keller et al, 1989;Cherry et al, 1991;Wagner et al, 1991;McCormac et al, 1993) and mutations in (Nagatani et al, 1991(Nagatani et al, , 1993Somers et al, 1991;Dehesh et al, 1993;Parks and Quail, 1993;Reed et al, 1993;Whitelam et al, 1993;Wagner and Quail, 1995;Xu et al, 1995) hypocotyl elongation, hook opening, and cotyledon expansion) in continuous far-red light (FRc), whereas phyB is primarily responsible for deetiolation in continuous red light (Rc). phyA is most abundant in dark-grown seedlings (m50-fold phyB levels), whereas, due to light-induced phyA degradation, phyB is more abundant in Rc (approximately twofold phyA) (Somers et al, 1991;.…”