Δ-carotene Research Articles

Differential content of leaf and fruit pigment in tomatoes culminate in a complex metabolic reprogramming without growth impacts

Although significant efforts to produce carotenoid-enriched foods either by biotechnology or traditional breeding strategies have been carried out, our understanding of how changes in the carotenoid biosynthesis might affect overall plant performance remains limited. Here, we investigate how the metabolic machinery of well characterized tomato carotenoid mutant plants [namely crimson (old gold-og), Delta carotene (Del) and tangerine (t)] adjusts itself to varying carotenoid biosynthesis and whether these adjustments are supported by a reprogramming of photosynthetic and central metabolism in the source organs (leaves). We observed that mutations og, Del and t did not greatly affect vegetative growth, leaf anatomy and gas exchange parameters. However, an exquisite metabolic reprogramming was recorded on the leaves, with an increase in levels of amino acids and reduction of organic acids. Taken together, our results show that despite minor impacts on growth and gas exchange, carbon flux is extensively affected, leading to adjustments in tomato leaves metabolism to support changes in carotenoid biosynthesis on fruits (sinks). We discuss these data in the context of our current understanding of metabolic adjustments and carotenoid biosynthesis as well as regarding to improving human nutrition.

Fruits from tomato carotenoid mutants have altered susceptibility to grey mold

The necrotrophic fungus Botritys cinerea takes advantage of the oxidative burst to facilitate tissue infection, leading to substantial losses during tomato postharvest. Tomato fruit is a source of carotenoids, pigments with a wide variety of isomeric configurations that determine their antioxidant capacity. Here, fruit susceptibility to B. cinerea was assessed in Micro-Tom Near Isogenic lines harboring mutations that alter the profile of carotenoids. Wound-inoculated fruit of the mutants Delta carotene (Del) and tangerine (t), which show large variety of carotenoids rather than the major accumulation of trans-lycopene, were less susceptible to the pathogen. Differences in susceptibility between the mutants were only observed in ripe fruit, after the formation of carotenoids, and they were associated with attenuation of damage caused by reactive oxygen species. The greater variety of carotenoid isomers, which in turn contributed to the greater lipophilic antioxidant capacity of fruit, was associated with the less susceptible mutants, Del and t. Together, our data reveals a potential activity of carotenoids in fruit defense, in addition to the well-known and widespread ecological role as attractors of seed dispersers.

Allelic variations in the tomato carotenoid pathway lead to pleiotropic effects on fruit ripening and nutritional quality

The accumulation of carotenoids is one of the main factors that determine the quality of tomato fruit. Variations in carotenoid biosynthesis genes found in some known tomato mutants such as yellow flesh (r), tangerine (t), Beta carotene (B) and Delta carotene (Del) alter the accumulation of carotenoids and lead to fruits with colors other than red at the end of ripening. Here, we used near-isogenic tomato lines carrying these allelic variations with the aim to compare their effect on fruit ripening and on the main quality parameters in a single genetic background (Micro Tom). Fruits were harvest in the mature green stage and monitored until the red ripe stage at 23 °C. Interestingly, besides the alteration of the carotenoid profile we also observed pleiotropic effects on fruit ripening. Fruit with loss of function of the PSY1 enzyme (r) had earlier and enhanced ethylene production, as well as accelerated fruit pigmentation. Another loss of function mutant, with reduced activity of the CRTISO enzyme (t), led to reduced ascorbic acid content and delayed fruit pigmentation. Fruit carrying gain of function in the activity of β-cyclase (B) and ε-cyclase (Del) enzymes showed thicker cuticle and enhanced ethylene production, respectively. We also observed that the presence of lycopene isomers and other carotenoid isoforms increased the antioxidant capacity of fruit to a higher extent when compared to the accumulation of a single major carotenoid. Together, these results suggest the involvement of carotenoids in events that regulate ripening and tomato fruit quality, and provide bases for the modification of their accumulation to obtain fruits with different quality and nutritional composition.

THE COMPETITIVE EFFECT OF THE BETA- AND DELTA-CAROTENE GENES ON ALPHA- OR BETA-IONONE RING FORMATION IN THE TOMATO

THE COMPETITIVE EFFECT OF THE BETA- AND DELTA-CAROTENE GENES ON ALPHA- OR BETA-IONONE RING FORMATION IN THE TOMATO