Abscisic acid deficiency in the tomato mutant high‐pigment 3 leading to increased plastid number and higher fruit lycopene content

Abstract

SummaryCarotenoids are present in most tissues of higher plants where they play a variety of essential roles. To study the regulation of carotenoid biosynthesis, we have isolated novel mutations in tomato (Solanum lycopersicum) with altered pigmentation of fruit or flowers. Here we describe the isolation and analysis of a tomato mutant, high-pigment 3 (hp3), that accumulates 30% more carotenoids in the mature fruit. Higher concentrations of carotenoids and chlorophyll were also measured in leaves and the pericarp of green fruit. The mutation in hp3 had occurred in the gene for zeaxanthin epoxidase (Zep), which converts zeaxanthin to violaxanthin. Consequently, leaves of the mutant lack violaxanthin and neoxanthin, and flowers contain only minute quantities of these xanthophylls. The concentration in the hp3 mutant of abscisic acid (ABA), which is derived from xanthophylls, is 75% lower than the normal level, making hp3 an ABA-deficient mutant. The plastid compartment size in fruit cells is at least twofold larger in hp3 plants compared with the wild-type. The transcript level in the green fruit of FtsZ, which encodes a tubulin-like protein involved in plastid division, is 60% higher in hp3 than in the wild-type, suggesting that increased plastid division is responsible for this phenomenon. Elevated fruit pigmentation and plastid compartment size were also observed in the ABAdeficient mutants flacca and sitiens. Taken together, these results suggest that ABA deficiency in the tomato mutant hp3 leads to enlargement of the plastid compartment size, probably by increasing plastid division, thus enabling greater biosynthesis and a higher storage capacity of the pigments.

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

“…5). This confirms previously reported data showing that PSY1 and PSY2 mRNA levels were lower in high-pigment mutants than the isogenic line at all the fruit ripening stages except fully-ripe in the hp-3 mutant (Galpaz et al 2008). ETR4 and ETR6, as PSY1, were strongly regulated by the genotype rather than by mycorrhization.…”

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

“…In the hp3 mutant, higher concentrations of carotenoids and chlorophyll were also measured in both leaves and the pericarp of green fruit. ABA deficiency in hp3 leads to an enlargement of plastid compartment size, probably by increasing plastid division, thus enabling greater biosynthesis and a higher storage capacity for the pigments (Galpaz et al, 2008). Our data indicate that overexpression of the tomato APRR2-Like gene is mediating its effect by both increasing the plastid size in the cells and the levels of chlorophyll and carotenoids.…”

“…A further mutation, hp3, shows an increase in plastid number and size and accumulates 30% more carotenoids than wild-type fruits. This effect has been mapped to a lesion in the zeaxanthin epoxidase gene, which results in a block in the biosynthesis of xanthophylls and greatly reduced levels of abscisic acid (ABA), xanthophylls being an essential precursor in the biosynthesis of this plant hormone (Galpaz et al, 2008). All of these hp mutations have deleterious effects on plant development, and because their effects are not fruit specific, they are difficult to harness effectively for crop improvement.…”

Gene and Metabolite Regulatory Network Analysis of Early Developing Fruit Tissues Highlights New Candidate Genes for the Control of Tomato Fruit Composition and Development

“…Until now, with the exception of the Nr mutant encoding an ethylene receptor (Wilkinson et al, 1995) and the hp3 mutation affecting an abscisic acid biosynthetic gene (Galpaz et al, 2008), the ripening mutations with known biochemical functions that have been identified affect signal transduction proteins, being either transcription factors (the MADS box and SBP box transcription factors) or proteins with a possible role in light signaling (DET1 and DDB1; Liu et al, 2004;Giovannoni, 2007;Wang et al, 2008). These studies further demonstrated that the alteration of a single regulatory gene may affect processes ranging from independent biosynthetic pathways controlling several phytonutrients (Davuluri et al, 2005;Wang et al, 2008) to whole developmental processes such as ripening.…”