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Elucidating the molecular basis of fruit resistance to desiccation: The cuticle as a key factor

Periodic Reporting for period 2 - 3F-FutureFreshFruit (Elucidating the molecular basis of fruit resistance to desiccation: The cuticle as a key factor)

Okres sprawozdawczy: 2017-09-15 do 2018-09-14

Water stress is a key environmental factor that, in a horticultural context, causes important quality and economical losses before and after fruit harvest. As water depletion is becoming increasingly problematic, improving water efficiency and tolerance of plants to dehydration is a priority of the European Union, as reflected in the societal challenge of Climate action, environment and resource efficiency. Likewise, food waste reduction is another key issue in the framework of Horizon 2020, as described in Food security and sustainable agriculture and forestry challenge. Indeed, a large proportion of fresh produce is wasted during postharvest (25-50%) of horticultural crops, which is largely caused by dehydration.

Therefore, this project deals with the urgent need of understanding factors influencing water loss to develop innovative solutions geared to saving water and reducing food waste.
Within this context, cuticular waxes are critical for limiting water loss from fruit, and thus for resisting desiccation and spoilage. We proposed to uncover the structural and regulatory pathways that mediate its biosynthesis, transport and assembly in response to drought stress by using tomato and citrus fruit as model systems.

We conclude that fruit cuticle properties are regulated along maturation process in an ABA-dependent way. Ripening stage and preharvest watering conditions are more important factors determining postharvest behaviour than the water stress conditions applied after fruit detachment. The outcomes of this proposal suggest strategies for enhancing shelf life, drought hardiness, water use efficiency and fruit quality in both climacteric and non-climacteric fruits.
The importance of fruit cuticle in water relations and firmness has been suggested through studies of the long-shelf life delayed fruit deterioration (dfd) tomato genotype. We tested the hypothesis that dynamic cuticle properties and composition affect tomato fruit transpiration and firmness and are influenced by environmental water availability, using dfd and two normally softening fruit cultivars, Ailsa Craig (AC) and M82, grown under control and water stress (WS) conditions. The effect of WS was also assessed following fruit detachment. WS increased fruit firmness, cuticle load, and the expression of cuticle biosynthetic genes, while reducing cuticle permeability and fruit transpiration rate in AC and M82, but not in dfd fruit. This study supports a direct relationship between fruit cuticle properties, transpiration and firmness, and provides insights into the adaptation of tomato genotypes to environments where water is scarce.

During the return phase, we studied the effect of abscisic acid (ABA) deficiency on cuticle formation along orange fruit development and maturation. We also tested whether postharvest ABA treatment can regulate cuticle properties and composition in citrus fruit and hence control fruit quality after detachment. In agreement with the results obtained with tomato fruit, orange fruit cuticle properties are regulated along maturation process and dependent on ABA content. Thus, ripening stage and preharvest conditions are more important factors determining postharvest behaviour than the water stress conditions applied after fruit detachment. We found these results especially relevant for the agricultural industry, since we claim that adjusting preharvest watering regime it is possible to regulate cuticle metabolism and properties and hence the postharvest behaviour of tomato and citrus fruit, two of the most important crops in the world.

In overview, we can learn from our results that water deficient regime conditions can improve tomato fruit quality after harvest through the modulation of cuticle-related molecular pathways. In addition, we found that ABA-deficiency is a factor increasing cuticle permeability and hence fruit weight loss in orange and tomato fruits. An innovative perspective of our project is considering the water stress growing conditions as a tool to improve fruit quality after harvest. Our experimental water deficient regime was able to increase the synthesis of cuticle components and hence reduce the transpiration rate and weight loss of the harvested tomatoes, which showed a better external appearance, fruit firmness and less decay. Therefore, such conditions led to increased tomato quality and reduced food waste. More research is needed to set up the related parameters, but our results will help to develop new strategies aimed to control fruit quality and shelf life of fleshy fruit in a harmful environment in which water is a scarce resource.
This proposal deals with subjects of importance for worldwide Agriculture and Food Science using cutting-edge technologies developed during this research. On one hand, this multidisciplinary research project provides results that will contribute to avoiding loss of fruit quality and, consequently, loss of economic value of fresh fruit. On the other hand, results obtained so far establish basic knowledge in tomato and citrus fruit for future development of biotechnological strategies aimed to enhance drought hardiness and water efficiency in horticultural crops and open new research lines focusing on disease resistance by improving epicuticular waxes, which will lead to reduction of pesticides. Both applied and basic research components are integral to those strategies that the EU are currently promoting, as reflected in Horizon 2020 designating the food security, sustainable agriculture and resources efficiency as key societal challenges.

Furthermore, translation of basic research into the breeding of drought-tolerant crops is a very important challenge for food security under global warming conditions. Because the global population continues to increase, and longevity has also been rapidly increasing, it is not only important for human health to increase food production but also to improve food quality. The successful application of basic knowledge from plant science and genomics will be crucial for future food security and agroindustry in the world. Such translational research for the production of more healthy and better foods is a visible contribution of plant science not only to European but also to worldwide society.

Our study has mainly focused on analyzing the impact of water stress environments in the metabolism and composition of the fruit cuticle and its relationship with the fruit quality after harvest. From the obtained results, we can learn that water deficient regime conditions can improve fruit quality after harvest through the modulation of cuticle-related molecular pathways. Although under our water stress conditions the size and productivity of the tomato plants was highly decreased, the shelf life period almost doubled, the pathogen infection was half reduced and the external appearance was improved, which is very relevant in a fleshy fruit such as tomato that displays a very short shelf life. In addition, we found that hormone deficiency, and more specifically ABA-deficiency is a factor increasing cuticle permeability and hence fruit weight loss in orange fruit. This fact highlights the relevance of ABA and cuticle properties for the postharvest performance of citrus fruit, pointing out the necessity of controlling fruit cuticle metabolism to avoid important economic losses due to fruit weight loss after harvest.
Final Report summary