ArabidopsisSHORT HYPOCOTYL UNDER BLUE1 Contains SPX and EXS Domains and Acts in Cryptochrome Signaling

Abstract

Photomorphogenesis is regulated by red/far-red light-absorbing phytochromes and blue/UV-A light-absorbing cryptochromes. We isolated an Arabidopsis thaliana blue light mutant, short hypocotyl under blue1 (shb1), a knockout allele. However, shb1-D, a dominant allele, exhibited a long-hypocotyl phenotype under red, far-red, and blue light. The phenotype conferred by shb1-D was caused by overaccumulation of SHB1 transcript and recapitulated by overexpression of SHB1 in Arabidopsis. Therefore, SHB1 acts in cryptochrome signaling but overexpression may expand its signaling activity to red and far-red light. Consistent with this, overexpression of SHB1 enhanced the expression of PHYTOCHROME-INTERACTING FACTOR4 (PIF4) under red light. PIF4 appears to specifically mediate SHB1 regulation of hypocotyl elongation and CHLOROPHYLL a/b BINDING PROTEIN3 or CHALCONE SYNTHASE expression under red light. Overexpression of SHB1 also promoted proteasome-mediated degradation of phytochrome A and hypocotyl elongation under far-red light. Under blue light, shb1 suppressed LONG HYPOCOTYL IN FAR-RED LIGHT1 (HFR1) expression and showed several deetiolation phenotypes similar to hfr1-201. However, the hypocotyl and cotyledon-opening phenotypes of shb1 were opposite to those of hfr1-201, and HFR1 acts downstream of SHB1. SHB1 encodes a nuclear and cytosolic protein that has motifs homologous with SYG1 protein family members. Therefore, our studies reveal a signaling step in regulating cryptochromeand possibly phytochrome-mediated light responses.

PIFs: Systems Integrators in Plant Development

“…In turn, in response to blue light attenuation, PIF4 and PIF5 have been proposed to promote growth downstream of cry through an unknown mechanism (Keller et al, 2011). Intriguingly, although PIFq members have been shown to inhibit seedling photomorphogenic development in blue light (Kang and Ni, 2006;Castillon et al, 2009;Kunihiro et al, 2010;Bu et al, 2011a), this effect appears to be mediated by phy, at least in the case of PIF1 and possibly PIF3 (Castillon et al, 2009;Bu et al, 2011a). By contrast, PIF4 and PIF5 have been shown to repress phototropism downstream of the blue light sensor phototropin (Sun et al, 2013).…”

Maize Source Leaf Adaptation to Nitrogen Deficiency Affects Not Only Nitrogen and Carbon Metabolism But Also Control of Phosphate Homeostasis

“…Particularly prominent seemed the role of SPX domain proteins in regulation of Pi homeostasis (for review, see Secco et al, 2012). However, differential regulation of SPX family members had also been found for Fe stress (Nakanishi et al, 1993), cold stress and osmotic stress (Zhao et al, 2009), N stress (Peng et al, 2007), and light stress (Kang and Ni, 2006). N-deficient maize leaves were characterized by high Pi concentration and significant down-regulation of six SPX domain-containing proteins and one significantly up-regulated member of the family.…”

Networks controlling seed size in Arabidopsis

“…SHB1 encodes a nuclear 220 SYG1-homologous protein (Kang and Ni 2006) that is 221 recruited by MINI3 to activate the IKU2 and MINI3 222 expression, and probably other genes required for endo-223 sperm development, stimulating the process of endosperm 224 cellularization (Kang et al 2013). SHB1 was first described 225 to be involved in hypocotyl development (Kang and Ni Article No.…”