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.
Abstract
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.
Objectives
It has been shown that epigenetics allows plants to adapt to environmental stress, and may ‘prime’ them to respond more rapidly to the same stress in the future.
This project aims to determine if long-term epigenetic memory of stress is passed on to cuttings taken in grapevine propagation and the applicability of using these cuttings in grapevine breeding.
Background
Epigenetics refers to the expression of genes in cells. The DNA sequence itself is not altered, but a chemical modification occurs to turn the gene ‘on’ or ‘off’.
These modifications survive cell division and can be passed onto the next generation.
Epigenetic memory could therefore be used to enhance plant resilience, while maintaining a level of plasticity which tends to be lost in lengthy conventional genetic breeding programmes.
For seed-propagated plants, the maintenance of epigenetic memory of stress has been shown to improve the offspring’s tolerance to stress. However, grapevines are propagated vegetatively and little is known on how vegetative propagation affects the epigenetic memory and long-term maintenance of stress-induced epigenetic modifications.
Approach
This research will build on the previous Wine Australia-funded incubator project (UA 1402), where a significant number of stress-induced epigenetic changes were maintained after plants reached physiological recovery once stress was discontinued; suggesting that epigenetic memory of stress is maintained in the grapevine.
This project will analyse to what extent the epigenetic memory of drought and heat stress (individually and combined) is maintained three and four years after discontinuation of the experienced stress.
Cuttings of Cabernet Sauvignon, exposed to stress in 2013 and analysed in the incubator project, will be re-exposed to stress and subject to analyses of physiological traits, epigenetic modification of genes and gene expression profiles (using established techniques).
In addition, the stressed plants will be propagated vegetatively using two methods, namely cuttings and layering, and analysed to test the heritability and durability of the epigenetic changes.
Sector benefits
The generation of new insights in the regulation of plant stress tolerance will provide tools to develop novel strategies for crop improvement. Priming donor plants before propagation could enhance water use efficiency and heat tolerance of new propagules, revolutionising breeding of grapevine varieties.
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