Xylem functionality controlling blossom-end rot incidence in transgenic ALC::NCED tomato plants

Abstract

Fruit susceptibility to the physiological disorder known as blossom-end rot (BER) is an important limitation in tomato production. Abscisic acid (ABA) is known to reduce leaf transpiration, which can enhance plant water use efficiency (WUE), as well as increase fruit xylem functionality, Ca2+ uptake and oxidative stress defenses, which has been suggested to reduce BER incidence. However, the role of ABA on most of these factors determining fruit susceptibility to BER remains poorly understood. ABA production is mainly regulated by the expression of 9-cis-epoxycarotenoid dioxygenase (NCED) genes. Manipulation of NCED gene expression by the alcohol inducible promoter (ALC) could be an alternative approach to stimulate ABA production and its beneficial effects on inhibiting BER incidence. The objectives of this study were to use ALC::NCED transgenic tomato plants to decrease BER incidence and investigate which mechanisms were involved in BER. In this study, two transgenic tomato lines (1 and 2) were developed with the ALC::NCED construct. This construct allows the inducible activation of the ALC promoter by treating the plants with ethanol vapor that drives NCED expression and ABA synthesis. According to the results, after full bloom, weekly spraying transgenic plants with ethanol (2%) decreased BER incidence in both transgenic lines, compared to the wild type ‘New Yorker’ plants. The transgenic line 1 had higher NCED expression in response to ethanol than the transgenic line 2 and wild type ‘New Yorker’. At 15 and 30 days after pollination, transgenic lines 1 and 2 had higher number of functional xylem vessels which helped to increase Ca2+ concentration in the distal end of the fruit, compared to the wild type fruit. In response to higher NCED expression, WUE and antioxidant content in leaves and fruit were higher in both transgenic lines, compared to the wild type, helping to explain the lower BER incidence. Therefore, our study shows that stimulating NCED expression with an inducible system increases the number of functional xylems and Ca2+ uptake into the fruit, improving plant WUE and reducing BER incidence.