Stress responses and comparative transcriptome analysis of Arabidopsis thaliana ecotypes exposed to BTEX compounds

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are important environmental pollutants around the world. The uptake and transformation of BTEX by plants are well understood, but not the molecular mechanisms for BTEX stress response. In the current study, we combined transcriptomic and physiology analysis of two Arabidopsis thaliana ecotypes with contrasting BTEX tolerance and subsequent validation using T-DNA knockout lines to identify BTEX-tolerance related genes. Physiology and gene expression were analyzed in seedlings exposed for 5 days to BTEX compounds separately and jointly. Our results showed reduced root length, high proline accumulation, and decreased chlorophyll content in the susceptible ecotype (Ct-1) after BTEX exposure, whereas the tolerant ecotype (Kn-0) did not show a statistically significant difference. A deep transcriptome revealed 1593, and 717 DEGs in Ct-1, and Kn-0, respectively, under BTEX stress, with 234 genes in common. DEGs associated with pathways such as "glutathione transferase activity" (GTSU4, GSTF3, GSTF6, GSLT1), "photosynthesis light harvesting in photosystem II" (LHCB2.1, LHCB2.2, and LHCB2.3), "cellular response to ethylene" (ETR2, Rap2, ORS1, NAC6), "biosynthesis of secondary metabolites" and "phenylpropanoid biosynthesis" (At1G49570) were found to be upregulated in Kn-0, and down-regulated in Ct-1 during stress. Also, we found two candidate genes such as basic region/leucine zipper motif 60 (BZIP60) (At1G42990) and a hypothetical protein (At2G16190) showing higher BTEX sensitivity in the T-DNA knockout mutants demonstrating their potential to function as positive regulators under BTEX stress.