RESUMO
Abscisic acid (ABA) is crucial for plant water deficit (WD) acclimation, but how the interplay between ABA and guard cell (GC) metabolism aids plant WD acclimation remains unclear. Here, we investigated how ABA regulates GC metabolism and how this contributes to plant WD acclimation using tomato wild type (WT) and the ABA-deficient sitiens mutant. These genotypes were characterized at physiological, metabolic, and transcriptional levels under recurring WD periods and were used to perform a13C-glucose labelling experiment using isolated guard cells following exogenously applied ABA. ABA deficiency altered the level of sugars and organic acids in GCs in both irrigated and WD plants and the dynamic of accumulation/degradation of these compounds in GCs during the dark-to-light transition. WD-induced metabolic changes were more pronounced in sitiens than WT GCs. Results from the 13C-labelling experiment indicate that ABA is required for the glycolytic fluxes toward malate and acts as a negative regulator of a putative sucrose substrate cycle. The expression of key ABA-biosynthetic genes was higher in WT than in sitiens GCs after two cycles of WD. Additionally, the intrinsic leaf water use efficiency increased only in WT after the second WD cycle, compared to sitiens. Our results highlight that ABA deficiency disrupts the homeostasis of GC primary metabolism and the WD memory, negatively affecting plant WD acclimation. Our study demonstrates which metabolic pathways are activated by WD and/or regulated by ABA in GCs, which improves our understanding of plant WD acclimation, with clear consequences for plant metabolic engineering in the future.
Assuntos
Ácido Abscísico , Solanum lycopersicum , Ácido Abscísico/metabolismo , Ácido Abscísico/farmacologia , Solanum lycopersicum/metabolismo , Solanum lycopersicum/genética , Estômatos de Plantas/metabolismo , Estômatos de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacosRESUMO
MAIN CONCLUSION: A first salt shock event alters transcriptional and physiological responses to a second event, being possible to identify 26 genes associated with long-term memory. Soil salinity significantly affects rice cultivation, resulting in large losses in growth and productivity. Studies report that a disturbing event can prepare the plant for a subsequent event through memory acquisition, involving physiological and molecular processes. Therefore, genes that provide altered responses in subsequent events define a category known as "memory genes". In this work, the RNA-sequencing (RNA-Seq) technique was used to analyse the transcriptional profile of rice plants subjected to different salt shock events and to characterise genes associated with long-term memory. Plants subjected to recurrent salt shock showed differences in stomatal conductance, chlorophyll index, electrolyte leakage, and the number of differentially expressed genes (DEGs), and they had lower Na+/K+ ratios than plants that experienced only one stress event. Additionally, the mammalian target of rapamycin (mTOR) pathways, and carbohydrate and amino acid-associated pathways were altered under all conditions. Memory genes can be classified according to their responses during the first event (+ or -) and the second shock event (+ or -), being possible to observe a larger number of transcripts for groups [+ /-] and [-/ +], genes characterised as "revised response." This is the first long-term transcriptional memory study in rice plants under salt shock, providing new insights into the process of plant memory acquisition.