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Leveraging the antioxidant role of volatile isoprenoids for improving grapevine resistance to ozone and temperature stress

Periodic Reporting for period 2 - OVOC (Leveraging the antioxidant role of volatile isoprenoids for improving grapevine resistance to ozone and temperature stress)

Reporting period: 2017-08-01 to 2018-07-31

Climatic changes are among the most striking phenomena of the present and future period. They are forecasted to lead to rising temperatures and ozone levels, and to an increased occurrence of extreme phenomena such as heat waves. It is therefore of utmost importance the understanding of how plants will react to such abiotic stresses and which phonotypic features are more likely to confer an increased resistance. This is especially relevant for crops such as grapevine, which is the most economically important fruit crop in Europe. In this context, the present project addresses the role of volatile isoprenoids, an important class of secondary metabolites produced by plants. It is believed that isoprenoids may have an antioxidant role in plants. For one isoprenoid, i.e. isoprene, this role has been proved but the underlying mechanism is unknown. There is still lack of knowledge for other isoprenoids. Some crops, grapevine for example, do not emit isoprene but emit other isoprenoids such as monoterpenes. The overall project objectives tackle these questions. First of all, an antioxidant mechanism for isoprene in plants is assessed. Specifically, it investigated if isoprene is oxidized within-plants, thus acting as scavenger of oxidants. Furthermore, the project aims at proving that volatile isoprenoids (likely monoterpenes) have an antioxidant role in grapevine. The present project demonstrated that monoterpenes are related to increased resistance to abiotic stress in grapevine. Therefore, it proved that the role isoprene has in other plants, is played by monoterpenes in grapevine. It also showed that the main underlying mechanism is not direct reaction of isoprenoids with oxidants.
In the first period of the project, it has been investigated if isoprene acts as antioxidant by directly reacting with oxidants inside plants. A relevant part of the work focused on a strong isoprene emitter, i.e. red oak, both in laboratory and in forest experiments. Existing literature suggests that the detection of isoprene oxidation products would prove within-plant isoprene oxidation. The emission of such products was therefore investigated in several conditions of abiotic stress using state-of-art detectors of volatile organic compounds. Experiments employing 13C labelled compounds were also carried out in order to track carbon. Fumigation experiments using oxidized isoprenoids were performed in order to check how plants reacts to these compounds. The latter experiments enhance the understanding of possible transformations that may occur within-plants to the oxidation products of isoprenoids. The role of volatile isoprenoids and the underlying mechanism was also investigated in grapevine by carrying out similar experiments. The results of the experiments were very positive and surprising. The reason why literature reports of isoprene oxidation products emission by plants are scarce was also unveiled as plants were shown to further metabolize such products. Some of the transformation products are volatiles and their detection was employed to strengthen the conclusions of isoprene oxidation. The emission of such product was established both in laboratory and forest experiments. But, by tracking carbon, it was demonstrated that such emissions were not linked to isoprene. It was thus shown that the mechanism underlying the antioxidant role of isoprene in plants is not direct reaction with oxidants. Several grapevine varieties were screened for abiotic stress resistance and monoterpene emission. Among them varieties having almost identical genetic background and only differing for a mutation on the monoterpene production pathway were included. It was proved that monoterpene emission relates to improved resistance to abiotic stresses in grapevine. The results have been presented at four conferences and in several publications in peer-reviewed international journals. They have also been presented in events for the general public, including two seminars. Given the outcomes, further exploitation by the scientific community is expected.
The project provided several results that go beyond the state of the art knowledge in the field. In particular, a transformation mechanism of the oxidation products of isoprene by plants was proposed and proved. Moreover, the emission of putative isoprene oxidation products and their transformation products upon abiotic stress was shown not be linked to within-leaf isoprene oxidation. The project also provided progress in the understanding of the role of volatile isoprenoids in grapevine and their link with grapevine resistance to abiotic stresses. It proved that monoterpene emission is causally linked to improved resistance in grapevine. The project is expected to have a socio-economic impact as it provides knowledge on a phenotypic trait and the corresponding genetic control conferring improved resistance to climatic changes to grapevines. Such information could be used by breeders developing new grapevine varieties and by farmers choosing which cultivars to grow. The scientific community will also benefit from the project results as, besides being relevant for a specific crop, they addressed some general open questions in science.