Over-expression of GGP and GPP genes enhances ascorbate content and nutritional quality of tomato

Authors: KOUKOUNARAS, ATHANASIOS - Aristotle University Of Thessaloniki; MELLIDOU, IFIGENEIA - Institute Of Plant Breeding And Genetic Resources; PATELOU, EFSTATHIA - Aristotle University Of Thessaloniki; KOSTAS, STEFANOS - Aristotle University Of Thessaloniki; SHUKLA, VIJAYA - Former ARS Employee; ENGINEER, CAWAS - Aristotle University Of Thessaloniki; PAPAEFTHIMIOU, DIMITRA - Aristotle University Of Thessaloniki; AMARI, FOUED - Aristotle University Of Thessaloniki; CHATZOPOULOS, DIMITRIS - Aristotle University Of Thessaloniki; Mattoo, Autar; KANELLIS, ANGELOS - Aristotle University Of Thessaloniki

Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2022
Publication Date: 11/1/2022
Citation: Koukounaras, A., Mellidou, I., Patelou, E., Kostas, S., Shukla, V., Engineer, C., Papaefthimiou, D., Amari, F., Chatzopoulos, D., Mattoo, A.K., Kanellis, A. 2022. Over-expression of GGP and GPP genes enhances ascorbate content and nutritional quality of tomato. Plant Physiology and Biochemistry. https://doi.org/10.1016/j.plaphy.2022.10.023.
DOI: https://doi.org/10.1016/j.plaphy.2022.10.023

Interpretive Summary: Ascorbic acid is an important molecule which has positive implications toward improving nutritional value in plants such as tomato. Thus, it has attracted considerable attention as a key molecule with different physiological responses. Our novel findings provide novel insights toward enhancing its endogenous levels in tomato fruit. These studies serve as breeding and gene editing targets for future trait improvement. The results obtained not only extend novel findings but also provide valuable information about tomato crop development, including genetic improvement programs. These studies are of interest to consumers, producers, scientists and tomato industry.

Technical Abstract: L-Ascorbic acid (AsA), a strong antioxidant, serves as an enzyme cofactor and redox status marker, modulating a plethora of biological processes. As commercial varieties and hybrids possess relatively low amounts of AsA in most fruit crop species, the improvement of fruit AsA represents a strategic goal for enhanced human health. Previously, we have suggested that GDP-L-Galactose phosphorylase (GGP) and L-galactose-1-phosphate phosphatase (GPP) can serve as possible targets for AsA manipulation in tomato (Solanum lycopersicon L.) fruit. To this end, we produced and evaluated T3 transgenic tomato plants carrying these two genes under the control of CaMV-35S and two fruit specific promoters, PPC2 and PG-GGPI. The transgenic lines were found to have elevated levels of AsA, with PG-GGP1 line containing 3-fold more AsA than WT. Following RNA-Seq analysis, 164 and 13 DEGs were up- or down-regulated, respectively, between PG-GGP1 and WT pink fruits, underlining a series of alterations in their gene expression profiles. PG-GGP1 fruit had a distinct number of up-regulated transcripts associated with cell wall modification, ethylene biosynthesis and signaling, pollen fertility and carotenoid metabolism. The elevated AsA accumulation resulted in the up regulation of AsA associated transcripts and alternative biosynthetic pathways suggesting that the entire metabolic pathway was influenced, probably via master regulation. We show here that AsA-fortification of tomato ripe fruit via GGP1 overexpression under the action of a fruit specific promoter PG affects fruit development and ripening, reduces ethylene production, and increased the levels of sugars, and carotenoids, supporting a robust database to further explore the role of AsA induced genes for agronomically important traits, breeding programs and precision gene editing approaches.