Characterising the memory effect of abiotic stresses in the adaptive response of plants

GOALS

MemoStress aims to quantify the adaptive responses to heat and water stress in two crop species (rapeseed and tomato), and to analyse the contribution of DNA methylation to the intra- and transgenerational memory of plants subjected to stress. In particular, the project aimed to:

1. Identify stress protocols generating a memory effect of heat or water stress on seed and fruit quality (rapeseed and tomato)
2. Evaluate the contribution of epigenetic marks in acclimatisation processes that can be transmitted to future generations.

Contrasting effects on the composition of tomato seeds, fruits and plants

In tomato, the first phenotypic analyses of the intragenerational memory effect indicate an impact of severe water deficit on development (delay that is not recovered) and the growth and composition of the plant organs, leading to a reduction in the fresh mass of fruits per plant but a weak effect on the total dry mass of the fruits. Gas exchange is reduced but the differences fade over time and in the long term, stressed plants show more efficient photosynthesis than control plants. Biochemical and molecular analyses are currently underway to better target the mechanisms involved and to assess the impact on fruit quality.

Overall, priming during the crop cycle seems to have some positive effects on the plant's ability to cope with a second water deficit and may therefore have effects that can be exploited to reduce water inputs (in greenhouses) or cope with repeated stresses (in the field). Moreover, the first results on the analysis of mutants show contrasting behaviours under water deficit conditions, with some showing little sensitivity, which could, following a more in-depth analysis, lead to applications in terms of selection.

The inter-generational memory effect of water deficit shows small and fairly specific variations. Overall, the origin of the seeds and the stress applied to the mother plant have little contrasted effects on the plant, but the first molecular analyses show fairly marked effects (in progress).

At the morphological level, the origin of the seed does not have a significant impact on the number and size of organs. Only the dry matter content of the fruits produced under water deficit conditions was significantly higher when the seeds came from stressed mother plants, suggesting an amplified effect in the second generation.

Gene expression analyses indicated that in response to water stress, expression profiles differed significantly between plants derived from unstressed plants and those derived from water-stressed parental plants, consistent with the idea of an intergenerational memory of stress. Conversely, under well-irrigated conditions, the plants have similar gene expression profiles, regardless of their parental origin.

 

A priming effect in rapeseed that depends on the intensity and period of stress and that does not affect second generation plants

Analyses of priming (a period of moderate stress preceding a series of thermal peaks) at the scale of the crop cycle indicated a positive effect on several grain quality criteria, such as seed nitrogen content and a soluble sugar ratio used to assess desiccation tolerance. For the other criteria, the application of this scheme had negative effects which tend to show a negative cumulative effect of the stress days (moderate pre-stress and thermal peaks) and not a priming effect allowing a mitigation of the negative effect of the peaks by the pre-stress. The underlying hypothesis is that the priming effect is highly dependent on the targeted compound (fatty acids, proteins, soluble sugars, hormones) and that the intensity of the pre-stress and its concomitance with the synthesis of the compound are decisive for generating the expected priming effect (Magno et al. 2021).

The analyses carried out on the seeds from the second generation of stressed plants showed mainly an effect of the stress applied to the seedling and not of the stress applied to the previous generation: the daughter effect is predominant over the mother effect. Overall, all the nutritional and physiological quality variables were negatively affected and the longer the stress (in cumulative duration) and/or the more intense it was, the higher the toll on quality. Germination rates are also subject to the history of the daughter and mother plants, indicating intergenerational effects (Magno et al. 2022).

Although it was not possible to identify thermo-sensitising patterns, our results tend to demonstrate the importance of the origin of the seed lots produced in the field and the interest in tracing the lots with a view to using them in favourable environments according to their production origin.