Résumé
In the light of climate change projections, heatwave events are expected to be more intense, last longer and occur more frequently (IPCC. 2021). Elevated temperatures severely affect plant performances in oilseed rape (Magno et al. 2021, 2022), and lead to changes at the transcriptome level (Jedličková et al. 2023). It is well established that an initial stress exposure can influence the response to subsequent stress through the storage and retrieval of stress-induced information, a phenomenon known as 'stress memory' (Crisp et al. 2016; Lamke and Baurle 2017), potentially leading to stress acclimation (Gallusci et al. 2023). Nevertheless, little is known about the features of stress sequences, and particularly the period between two stress events that induce “acquired thermotolerance”. In our study we conducted a controlled-environment experiment on Brassica napus (cv. Aviso) under three stress recurring scenarios that differed in the time interval between the first stress (mild) and the second stress (heat peaks) to answer the following questions: a) What are the differences in gene expression following one isolated heat stress or recurring stresses ? b) Are there genes whose expression is maintained between two stress events i.e. during the recovery phase? c) Are there memory genes that can affect the plant's responses in either a positive or negative manner ? Due to the indeterminate growth pattern, leading to co-occurrence of flowers, developing and maturing pods during the stress, the plants were divided into three pod cohorts at the maturation stage, when the heat stress were applied at GS72 (i.e. 20% fully developed pods) to avoid any plant age effect. Pods were harvested at different timing over the heat stress periods and separated in order to collect material for RNAseq analysis of seeds and pericarps. Sequencing was performed using Illumina technology, with reads aligned to the Brassica napus (Darmor-bzh) genome. Differential expression analysis was performed using DIANE (https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-021-07659-2) (FDR ≤ 0.05 and |Log₂ Fold Change| ≥ 0.5). Therefore, we postulate that genes related to heat stress will be identified at key points of the heat sequences, and will be recognised as memory genes.