Análise temporal transcricional da rota metabólica de antocianinas em frutos de tomateiro expostos à luz

Abstract

Anthocyanins are phenolic compounds derived from the phenylpropanoids pathway. They belong to the class of flavonoids of the specialized metabolism of plants. These pigments are responsible for the coloring of fruits, flowers, and leaves of various plants and are highlighted as an antioxidant component of the diet that is beneficial to human health. In cultivated varieties of tomato (Solanum lycopersicum), the levels of anthocyanins in the fruits are virtually nonexistent, but some species of wild tomatoes develop pigmented (cyanic) fruit. Through interspecific crossings, this trait was previously transferred to the cultivated tomato. The combination of different natural alleles responsible for anthocyanin biosynthesis (AFT and ATV) through classical breeding led to selecting a tomato lineage showing a purple color in epidermal cells of the fruit, but with the pulp (mesocarp) still showing negligible levels of anthocyanins. The accumulation of anthocyanin in the fruits usually requires light, but the kinetics of this accumulation is not well characterized in tomato. At the molecular level, the anthocyanin biosynthesis is regulated by coordinated transcriptional control of the structural enzymes on the biosynthetic via the ternary complex MBW, consisting of R2R3-MYB, bHLH, and WD40 transcript factors. Changes in light conditions alter the expression levels of these transcription factors, especially R2R3-MYB, which is adjusted to regulate anthocyanin biosynthesis. Previous studies carried out in our laboratory with the triple mutant Aft/atv/hp2 indicated that anthocyanin accumulation begins in the epidermis of the fertilized ovary shortly after exposure to light. These results led us to carry out new studies to get a better understanding of the regulatory mechanism. Given the importance of light to activate some anthocyanin regulatory genes in fruits and vegetables and a better understanding of the regulatory biosynthetic mechanism and accumulation of anthocyanins in tomato fruits, we used RNA-Seq to investigate the kinetics of the light-mediated regulation of the genes of the biosynthesis pathway of anthocyanins. This study demonstrated that the lack of pigmentation in the mesocarp cells is related to the lack of expression of the bHLH transcription factor SlAN1. The initial pigmentation in epicarp cells seems to establish a filter that impairs the intensity and quality of light reaching the mesocarp cells, thus preventing them from expressing the gene SlAN1, which is induced by light and possibly by developmental cues.