The FUSCA genes of Arabidopsis: negative regulators of light responses

Abstract

More than 200 fusca mutants of Arabidopsis have been isolated and characterised, defining 14 complementation groups. Mutations in at least nine FUSCA genes cause light-dependent phenotypic changes in the absence of light: high levels of anthocyanin accumulation in both the embryo and the seedling, inhibition of hypocotyl elongation, apical hook opening, and unfolding of cotyledons. In double mutants, the fusca phenotype is epistatic to the hy phytochrome-deficiency phenotype, indicating that the FUSCA genes act downstream of phytochrome. By contrast, the accumulation of anthocyanin is suppressed by mutations in TT and TTG genes, which affect the biosynthesis of anthocyanin, placing the FUSCA genes upstream of those genes. Regardless of the presence or absence of anthocyanin, fusca mutations limit cell expansion and cause seedling lethality. In somatic sectors, mutant fus1 cells are viable, expressing tissue-specific phenotypes: reduced cell expansion and accumulation of anthocyanin in subepidermal tissue, formation of ectopic trichomes but no reduced cell expansion in epidermal tissue. Our results suggest a model of FUSCA gene action in light-induced signal transduction.

Photosynthetic sucrose acts as cotyledon-derived long-distance signal to control root growth during early seedling development in Arabidopsis

“…Instead, Fig. 4A shows that the roots of cop1-4 seedlings are short, indicating that primary root growth does not follow the photomorphogenic program executed in the shoot via the light-mediated elimination of COP1 function, in line with observations of Miséra et al (15).…”

The role of COP1 in light control of Arabidopsis seedling development

“…One of the most interesting developments in recent pleiotropic copldet mutant studies is the demonstration that the pleiotropic COPIDET loci are allelic to FUSCA {FUS) loci (Castle & Meinke 1994;Misera et al 1994;Kwok et al 1996). All /w.v mutants were identified through a genetic screen for purple seed colour (due to high-level accumulation of anthocyanin in cotyledons of the mature seeds) and are lethal after the seedling stage (Castle & Meinke 1994;Misera et al 1994).…”

“…All /w.v mutants were identified through a genetic screen for purple seed colour (due to high-level accumulation of anthocyanin in cotyledons of the mature seeds) and are lethal after the seedling stage (Castle & Meinke 1994;Misera et al 1994). Thus, all pleiotropic COPIDETIFUS genes represent genes that not only repress photomorphogenesis in darkness but are also essential for completion of the life cycle of Arabidopsis under norrnal light conditions.…”

The Role of the COP/DET/FUS Genes in Light Control of Arabidopsis Seedling Development

“…Mutants in the first group have so far been identified in severa1 Arabidopsis loci (copl, detl, and cop8-15) (Chory et al, 1989;Deng et al, 1991;Wei and Deng, 1992;Wei et al, 1994b;Miséra et al, 1994;Kwok et al, 1996). These mutants exhibit a lightindependent pleiotropic phenotype: dark-grown seedlings resemble their light-grown siblings in overall morphology, cell and plastid differentiation, and expression pattern of light-regulated genes.…”

“…Whereas cop2 and cop3 do not significantly affect light-regulated gene expression, cop4 shows moderate de-repression of nuclearencoded light-induced gene expression (CAB1, chlorophyll alb-binding protein) in the dark (Hou et al, 1993). Wei et al, 1994Wei et al, 1994Castle andMeinke, 1994 Miséra et al, 1994;Kwok et al, 1996Miséra et al, 1994Kwok et al, 1996Miséra et al, 1994Kwok et al, 1996Miséra et al, 1994Kwok et al, 7 996 Chory et al, 1989Hou et al, 1993Lehman et al, 1996;Chaudhury et al, 1993Hou et al, 1993Lehman et al, 1996Hou et al, 1993Lehman et al, 1996Chory et al, 1991 Cabrera y Poch et al., 1993Desnos et al, 1996Takahashi et al, 1995Szekeres et al, 1996 The primary seedling phenotype of the third group is a short hypocotyl when grown in darkness for less than 5 d (det2, det3, dim, prcl, cpd) (Chory et al, 1991;Cabrera y Poch et al, 1993;Takahashi et al, 1995;Desnos et al, 1996;Szekeres et al, 1996). Significant cotyledon expansion and opening also occurred after extended dark growth (more than 1 week) in most of those mutants (except p y c l ) , although no sign of chloroplast development was observed.…”