Epigenetic mechanisms are an interface between the environment and the plant genotype (the plant’s collection of genes) that regulate gene expression in response to changing environments. When the epigenetic ‘memory’ of stress improves the response to subsequent stress, the plant is said to be epigenetically primed. We exposed Cabernet Sauvignon plants to drought, heat and combined drought and heat stresses and monitored their physiological responses and gene expression. These plants were propagated via different methods and subsequently re-challenged with combined drought and heat stress in the following year, together with the original plants. Environmental stresses had a significant impact on the plants’ gene expression in both experiments and the profile of expression was different with each of the stresses. However, there was no effect of prior stress exposure on vine physiological response during vegetative growth.
Although drought and high temperature stress often occur together in the summer, and heatwave incidents will occur more frequently with climate change, the effect of the combination of these two stresses on grapevine has rarely been studied. We grew Cabernet Sauvignon plants in two years where plants were exposed to drought alone, heat stress alone, and the combination of the two stresses in year 1. Plants were then propagated, either from dormant buds or by layering, and exposed to the dual stress in the second year.
We found that plant growth was affected by each of the stresses and that the effect of heat on top of drought was more than just additive. Plant gene expression was more sensitive following combined stress treatment than in either stress alone i.e. more genes were up- and down-regulated.
We also found that plant gene expression was more sensitive to drought and heat stress in plants propagated by layering than from dormant buds. However, there were no significant differences in plant growth between the two propagation methods during the vegetative phase and there was no effect of the previous year’s exposure on any of the stresses after propagation by either method.
We recommend that future research is directed to the combination of drought and heat stress on grapevine and that the effects of the changes in gene expression on final yield and berry quality are investigated.
The genes changing expression in common in each of the treatments are likely to be important for response and adaptation to the stresses. Genes in heat shock response pathways and sugars metabolism were over-represented in this category and any genetic variation in these genes could be useful for the breeding of improved varieties to cope with climate change.