Heat tolerance and the regulation of climacteric fruit ripening

Tomato, Solanum lycopersicum, is one of the major fruit with the worldwide production of 171 million tons in 2014 (FAOSTAT, 2017). With the production of 210301 tons and a turnover of 159 million Euro in 2016, tomato is considered as the most important fruit commercialized by Belgian auctions (VBT, 2017). In Vietnam, tomato has become a notable export. The cultivation area in Vietnam is about 25483 ha with an average yield of 28.7 tons/ha which is higher than that of other countries in the South Asian region (STATS, 2013). In the past, tomato was grown only in the favorable season (winter time) and harvested in a short time, causing the low price. Meanwhile, there is a shortage of tomato and its price is 2 to 3 time higher in the summer. In recent years, heat-tolerant cultivars have been introduced to Vietnam and the situation has been improved, but there is still a low supply between June and September. Tomato which is heat sensitive/tolerant is generally based on its performance of plant growth, flower initiation, fruit development and ripening. Most researches focus on hybridization, disease control, and grafting. Less is known about genetic differences influencing the ripening and postharvest behavior of the fruit. Fruits are non-climacteric or climacteric based on the extraordinary increment in ethylene production at the onset of ripening. A climacteric fruit is characterized by a burst in ethylene production which accompanies the respiratory peak during ripening, called the 'climacteric crisis' (Abeles et al.,1992). Tomato is known as the basic and scientific model system for climacteric fruit development and ripening as it is easily propagated, transformed, self-pollinated. Not only that, there is a wide range of public resources and the genome database/ transcriptomic profiles are available. Ethylene is a key hormone as it not only induces fruit ripening but also regulates distinct physiological and morphological responses in plants (leaf abscission, biotic defense against pathogen infection, response to abiotic stress, etc.). This implies that differences in ethylene biosynthesis and signaling pathway affect the ripening process (Rugkong et al., 2011).  Among heat-tolerant cultivars, 'Savior' variety is thoroughly paid attention due to its high yield performance, good appearance, disease-resistance, and excellent eating quality. Some studies investigated the improvement of cultivating technique, and optimization of post-harvest conditions. At present, there is no information regarding the regulation of climacteric ripening of heat-tolerant cultivar at the level of ethylene biosynthesis and signaling. Therefore, the goals of this study are (i) to understand the underlying regulation of climacteric ripening of heat-tolerant/sensitive tomato at the level of ethylene perception and signaling and (ii) to model the ethylene biosynthesis and signaling pathways during climacteric ripening of tomato fruit. The complexity of the ethylene biosynthesis and signaling pathways and their interaction as well as the regulation of fruit ripening of heat-tolerant tomato will be characterized.