RESUMO
Climate change has been shown to have a substantial impact on agriculture and high temperatures and heat stress are known to have many negative effects on the vegetative and reproductive phases of plants. In a previous study, we addressed the effects of high temperature environments on olive oil yield and quality, by comparing the fruit development and oil accumulation and quality of five olive cultivars placed in high temperature and moderate temperature environments. The aim of the current study was to explore the molecular mechanism resulting in the negative effect of a high temperature environment on oil quantity and quality. We analyzed the transcriptome of two extreme cultivars, 'Barnea', which is tolerant to high temperatures in regard to quantity of oil production, but sensitive regarding its quality, and 'Souri', which is heat sensitive regarding quantity of oil produced, but relatively tolerant regarding its quality. Transcriptome analyses have been carried out at three different time points during fruit development, focusing on the genes involved in the oil biosynthesis pathway. We found that heat-shock protein expression was induced by the high temperature environment, but the degree of induction was cultivar dependent. The 'Barnea' cultivar, whose oil production showed greater tolerance to high temperatures, exhibited a larger degree of induction than the heat sensitive 'Souri'. On the other hand, many genes involved in olive oil biosynthesis were found to be repressed as a response to high temperatures. OePDCT as well as OeFAD2 genes showed cultivar dependent expression patterns according to their heat tolerance characteristics. The transcription factors OeDof4.3, OeWRI1.1, OeDof4.4 and OeWRI1.2 were identified as key factors in regulating the oil biosynthesis pathway in response to heat stress, based on their co-expression characteristics with other genes involved in this pathway. Our results may contribute to identifying or developing a more heat tolerant cultivar, which will be able to produce high yield and quality oil in a future characterized by global warming.
RESUMO
Global warming is predicted to have a negative effect on plant growth due to the damaging effect of high temperatures. In order to address the effect of high temperature environments on olive oil yield and quality, we compared its effect on the fruit development of five olive cultivars placed in a region noted for its high summer temperatures, with trees of the same cultivars placed in a region of relatively mild summers. We found that the effects of a high temperature environment are genotype dependent and in general, high temperatures during fruit development affected three important traits: fruit weight, oil concentration and oil quality. None of the tested cultivars exhibited complete heat stress tolerance. Final dry fruit weight at harvest of the 'Barnea' cultivar was not affected by the high temperature environment, whereas the 'Koroneiki', 'Coratina', 'Souri' and 'Picholine' cultivars exhibited decreased dry fruit weight at harvest in response to higher temperatures by 0.2, 1, 0.4 and 0.2 g respectively. The pattern of final oil concentration was also cultivar dependent, 'Barnea', 'Coratina' and 'Picholine' not being affected by the high temperature environment, whereas the 'Koroneiki' and 'Souri' cultivars showed a decreased dry fruit oil concentration at harvest under the same conditions by 15 and 8% respectively. Regarding the quality of oil produced, the 'Souri' cultivar proved more tolerant to a high temperature environment than any other of the cultivars analyzed in this study. These results suggest that different olive cultivars have developed a variety of mechanisms in dealing with high temperatures. Elucidation of the mechanism of each of these responses may open the way to development of a variety of olives broadly adapted to conditions of high temperatures.