Grapevine adaptations to drought stress: proposed mechanisms and methods for investigation.

Grapevines control the hydration of their organs [1,2,3], by regulating absorption of water from the soil [3,4,5], its transport within the plant [6,7,8,9,10] and its loss by evaporation from the leaves [11,12]. Adaptation of grapevines to water deficit is a wide and complex biological process [13] that implies global changes in plant hydraulics [14,15], in signaling among plant organs [15,16], in gene expression [17,18,19] and in primary and secondary metabolite biosynthesis and accumulation [20]. Research application aims to understand how plant hormone and/or hydraulic drought signals, driving ecophysiological grapevine adaptation to water availability with consequences on secondary metabolite accumulation, could determine fruit quality [20]. In grapevine, rootstock, via its capacity of water extraction from the soil, and scion, via its sensitivity of the stomatal control, concur to whole-plant resistance to drought [14,21]. Plant components interact through a complex of hydraulic (xylem embolism formation and repair) [3,21], hormonal (especially abscisic acid, ABA)[15,16,20] and molecular (miRNAs) [22] signal exchanges occurring between roots and leaves. In addition, in rain-fed vineyards, soil water-holding capacity [4,5] is reputed to control the productive potential additively to and even more than rootstock and scion [23]. In these contexts, xylem development [6,7], whole plant hydraulic conductance [1,3,15,19], and plant control of xylem embolism [10,14,16,17,18] are followed as influenced by grapevine genotypes [11] and water-holding soil capacities [4,5,23]. The relationship between the expression of ABA biosynthesis genes, the accumulation of ABA in leaf [15,16] and in berry and the promotion of berry ripening by ABA is studied [20]. The role of ABA is seen as a link between berry ripening process and grapevine response to stress [13]. Ongoing research focuses on understanding the contribution of aquaporins on regulating water use efficiency following experience in model plants related to both water and carbon dioxide metabolisms [24,25], an expected interaction between strigolactones and ABA under abiotic stress [26,27,28], and carbon delivery in grape organs during drought and rehydration periods. Acknowledgements: CARBOSTRESS project - CRT Foundation. 1] Vitali et al. 2016 Physiologia plantarum, doi: 10.1111/ppl.12463 2] Kaldenhoff et al. 2008 Plant Cell Env, doi: 10.1111/j.1365-3040.2008.01792.x 3] Perrone et al. 2012 Plant Physiology, doi: 10.1104/pp.112.203455 4] Tramontini et al. 2013 Plant and Soil, doi: 10.1007/s11104-012-1507-x 5] Tramontini et al. 2014 Functional Plant Biology, doi: 10.1071/FP13263 6] Lovisolo & Schubert 1998 Journal of Experimental Botany, doi: 10.1093/jxb/49.321.693 7] Schubert et al. 1999 Plant, Cell & Environment, doi:10.1046/j.1365-3040.1999.00384.x 8] Lovisolo & Schubert 2000 Vitis , http://hdl.handle.net/2318/6645 9] Lovisolo et al. 2002 New Phytologist, doi:10.1046/j.1469-8137.2002.00492.x 10] Lovisolo & Schubert 2006 New Phytologist, doi:10.1111/j.1469-8137.2006.01852.x 11] Lavoie-Lamoureux et al. 2017Physiologia plantarum, doi: 10.1111/ppl.12530 12] Pou et al. 2008 Physiologia plantarum, doi: 10.1111/j.1399-3054.2008.01138.x 13] Lovisolo et al. 2010 Functional Plant Biology, doi: 10.1071/FP09191 14] Lovisolo et al. 2008 Env Exp Bot, doi:10.1016/j.envexpbot.2007.11.005 15] Lovisolo et al. 2002 Functional Plant Biology, doi:10.1071/FP02079 16] Lovisolo et al. 2008 New Phytologist, doi: 10.1111/j.1469-8137.2008.02592.x 17] Perrone et al. 2012 Planta, doi: 10.1007/s00425-011-1581-y 18] Chitarra et al. 2014 Planta, doi: 10.1007/s00425-013-2017-7 19] Pantaleo et al. 2016 Scientific Reports, doi:10.1038/srep20167 20] Ferrandino & Lovisolo 2014 Env Exp Bot, doi: 10.1016/j.envexpbot.2013.10.012 21] Tramontini et al. 2013 Env Exp Bot, doi: 10.1016/j.envexpbot.2013.04.001