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Loss-of-function of PHYTOENE synthase and its relation to the ethylene and abscisic acid pathway during the postharvest ripening of tomato fruit

Grant number: 19/01156-0
Support type:Regular Research Grants
Duration: May 01, 2019 - April 30, 2021
Field of knowledge:Biological Sciences - Botany
Principal Investigator:Ricardo Alfredo Kluge
Grantee:Ricardo Alfredo Kluge
Home Institution: Escola Superior de Agricultura Luiz de Queiroz (ESALQ). Universidade de São Paulo (USP). Piracicaba , SP, Brazil
Assoc. researchers: Ana Paula Preczenhak ; Eduardo Purgatto ; Ivan Sestari ; Lázaro Eustaquio Pereira Peres ; Neuza Mariko Aymoto Hassimotto

Abstract

Carotenoids are important pigments accumulated in large amounts in tomato fruit. The first step of carotenogenesis is catalyzed by the fruit-specific enzyme PSY1 (PHYTOENE SYNTHASE 1) and leads to the formation of phytoene from geranyl geranyl diphosphate (GGPP). This is the rate-limiting step of the pathway, precisely because it provides the first carotenoid, and also by the competition of GGPP with other important metabolic pathways that use it as a substrate for the formation of chlorophylls, tocopherols and gibberellins. In this sense, the manipulation of the PSY1 isoform has been the target of genetic engineering, due to its central role in directing the metabolic flow through the carotenoid biosynthesis pathway. However, this manipulation has shown to impact not only the carotenoid content, but also other important pathways for plant development. Recently, we have observed the occurrence of new pleiotropic effects in fruits of the yellow flesh mutant, where the PSY1 isoform is not functional. Surprisingly, we found higher ethylene production, accelerated maturation and early abscission of the fruits, which is counter intuitive since there is no direct link of PSY1 to the ethylene biosynthesis pathway. As a result, we hypothesized that changes in ethylene sensitivity and / or signaling in fruits may be involved with these responses. In addition, considering that carotenoids are precursors of ABA synthesis, the absence of these pigments may have altered the endogenous concentration of this hormone, modifying the hormonal balance between ABA and ethylene in the fruit, and leading to the occurrence of such pleiotropic effects. In order to elucidate these issues, this project proposes to characterize molecularly and physiologically the pleiotropic effects associated with the accelerated maturation of the fruits in the mutant yellow flesh and to determine its relation with the loss-of-function of the enzyme phytoene synthase (PSY1). Subsequently, we will seek to determine if there is a causal relationship between the new pleiotropic effects characterized in yellow flesh with possible perturbations in the ABA biosynthesis pathway, which, dependent on precursors from the carotenoid pathway. This proposal, in addition to being relevant as a basic research, could generate information of immediate applicability for postharvest, a topic of great economic and strategic importance for agriculture. (AU)