Phenotype of the Tomato high pigment-2 Mutant Is Caused by a Mutation in the Tomato Homolog of DEETIOLATED1

Abstract

Tomato high pigment ( hp ) mutants are characterized by their exaggerated photoresponsiveness. Light-grown hp mutants display elevated levels of anthocyanins, are shorter and darker than wild-type plants, and have dark green immature fruits due to the overproduction of chlorophyll pigments. It has been proposed that HP genes encode negative regulators of phytochrome signal transduction. We have cloned the HP-2 gene and found that it encodes the tomato homolog of the nuclear protein DEETIOLATED1 (DET1) from Arabidopsis. Mutations in DET1 are known to result in constitutive deetiolation in darkness. In contrast to det1 mutants, tomato hp-2 mutants do not display any visible phenotypes in the dark but only very weak phenotypes, such as partial chloroplast development. Furthermore, whereas det1 mutations are epistatic to mutations in phytochrome genes, analysis of similar double mutants in tomato showed that manifestation of the phenotype of the hp-2 mutant is strictly dependent upon the presence of active phytochrome. Because only one DET1 gene is likely to be present in each of the two species, our data suggest that the phytochrome signaling pathways in which the corresponding proteins function are regulated differently in Arabidopsis and tomato. INTRODUCTIONLight is a critical environmental signal controlling many aspects of plant development. For example, dark-grown plants display a typical etiolated morphology with elongated hypocotyls, closed apical hooks, and unexpanded cotyledons, whereas plants grown in the light have short hypocotyls, opened apical hooks, and expanded photosynthetically active cotyledons. Light is perceived by a series of photoreceptors that can detect light within a wide spectral range. The phytochromes are the best characterized of these photoreceptors and are able to intercept light primarily within the red and far-red regions of the spectrum (Furuya and Schäfer, 1996). They exist as multigene families, for example, PHYA to PHYE in Arabidopsis, and each phytochrome is likely to have a specific photoperceptory function during plant development (Quail et al., 1995). In addition, plants contain blue/UV-A-absorbing cryptochromes and UV-Babsorbing photoreceptors.Several models for light signal transduction in plants have been proposed. One has been deduced largely by microinjection experiments with tomato and involves G proteins, calcium, and cGMP (Bowler et al., 1994b;Mustilli and Bowler, 1997). Others are based on the genetic analysis of Arabidopsis mutants, such as deetiolated ( det ) and constitutively photomorphogenic ( cop ), which display characteristics of light-grown plants when grown in complete darkness, for example, reduced hypocotyl length, cotyledon opening and expansion, chloroplast development, and expression of light-induced genes (Chory et al., 1989(Chory et al., , 1996Deng et al., 1991;Chamovitz and Deng, 1996).Although several COP and DET genes have been identified, it is not clear how the activities of their gene products are regulated by phytochrome or by the calcium-an...

Gr and hp-1 tomato mutants unveil unprecedented interactions between arbuscular mycorrhizal symbiosis and fruit ripening

“…2). The fruit phenotype of the two mutant lines confirmed previous characterizations (Mustilli et al 1999;Barry and Giovannoni 2006). Hp-1 fruits monitored at the same ripening stage as WT showed enhanced fruit and leaf pigmentation, comparable to data reported in the tomato Genetics Resources Center database (http://tgrc.ucdavis.edu/Data/Acc/GenDetail.aspx?Gene=hp-1).…”

Carotenoids and Photosynthesis - Regulation of Carotenoid Biosyntesis by Photoreceptors

“…Post transcriptional gene silencing of det1 leads to an accumulation of carotenoids in tomato fruits (Davuluri et al, 2005). Highly pigmented tomato mutants, hp1 and hp2 display shortened hypocotyls and internodes, anthocyanin accumulation, strongly carotenoid colored fruits and an excessive response to light (Mustilli et al, 1999). HP1 and HP2 encode the tomato orthologs of DDB1 and DET1 in A. thaliana, respectively (Liu et al, 2004).…”

Network Inference Analysis Identifies an APRR2-Like Gene Linked to Pigment Accumulation in Tomato and Pepper Fruits

“…These include highpigment1 (hp1), which harbors a lesion in UV-DAMAGED DNA-BINDING PROTEIN1 (DDB1; Lieberman et al, 2004;Liu et al, 2004), and hp2, a mutation in tomato DEETIOLATED1 (DET1; Mustilli et al, 1999). These genes are involved in the suppression of light responses in the absence of light, and for DET1, this is by a molecular mechanism involving chromatin remodeling (Davuluri et al, 2004).…”