Decifrando a tolerância à salinidade em plantas: análise de promotores, genes candidatos e o sistema de defesa antioxidante

Abstract

Soil salinity poses an increasing obstacle to global agriculture, affecting over 100 countries across all continents. This abiotic stress negatively impacts crops, reducing productivity and threatening food security. In this scenario, the search for effective solutions to ensure the sustainability of agricultural production becomes crucial. In this context, transcriptomics emerges as a powerful tool to investigate the complex molecular responses of plants to salinity. Transcriptomics, through the RNA-Seq technique, also known as whole transcriptome shotgun sequencing, allows for the detailed characterization of the transcriptome in a cell, tissue, or organism at a specific time. This technology enables the identification of most genes expressed at a specific stage, the differentiation of different isoforms, and the quantification of transcript expression levels. To validate RNA-Seq results, other techniques such as quantitative real-time PCR (qRT-PCR) can be employed. This study explores the complex response of the antioxidant defense system in two salt-tolerant species: purslane (Portulaca oleracea L.) and gliricidia (Gliricidia sepium (Jacq.) Kunth) acclimated to extreme salt stress. The study focused on a pre-selected group of genes encoding key antioxidant enzymes and redox molecules, recognized for their crucial role in the plant's antioxidant defense system. These genes were investigated using qRT-PCR, phylogenetic analysis, and additional structural and functional characterization. Purslane results revealed significant upregulation of four antioxidant enzymes and two redox molecules specifically in salt-stressed leaves, not in roots. This finding suggests that differential regulation of the antioxidant system in leaves contributes to purslane's salt tolerance. Gliricidia results highlight the regulatory mechanisms governing antioxidant enzymes and redox molecules in plants adapted to very high salt stress, evidencing a predominant role of the root system in this response. This finding paves the way for future research on the crucial role of roots in the salt tolerance of this species. Oil palm results demonstrated that transcriptome analysis led to the selection of 14 genes that underwent structural and functional annotation, in addition to having their expression validated by qRT-PCR. These studies represent a pioneering application of RNA-Seq and qRT-PCR to unravel the contribution of the antioxidant defense system to the remarkable resilience of purslane and gliricidia to high salt stress. The oil palm study helped validate the process of accurate selection of salt stress-responsive genes with a specific and predefined expression profile and their promoter sequence. These results represent an important step towards identifying key genes for the development of salt-tolerant oil palm.