Physio-biochemical and DNA methylation analysis of the defense response network of wheat to drought stress.

In the present work, physio-biochemical and DNA methylation analysis were conducted in wheat (Triticum aestivum L.) cultivars "Bolani" (drought-tolerant) and "Sistan" (drought-sensitive) during drought treatments: well-watered (at 90% field capacity (FC)), mild stress (at 50% FC, and severe stress (at 25% FC). During severe stress, O2•- and H2O2 content in cultivar Sistan showed significant increase (by 1.3 and 2.5-fold, respectively) relative to cultivar Bolani. In Bolani, the increased levels of radical scavenging activity (by 32%), glycine betaine (GB) (by 11.44%), proline (4-fold), abscisic acid (by 63.76%), and more stability of relative water content (RWC) (2-fold) were observed against drought-induced oxidative stress. Methylation level significantly decreased from 70.26% to 60.64% in Bolani and from 69.06% to 59.85% in Sistan during stress, and higher decreased tendency was related to CG and CHG in Bolani but CG in Sistan under severe stress. Methylation patterns showed that the highest polymorphism in Bolani was mainly as CG. As the intensity of stress increased, the enhanced physio-biochemical responses of Bolani cultivar were accompanied by a more decrease in the number of unchanged bands. According to heat map analysis, the highest difference (84.38%) in methylation patterns was observed between control and severe stress. Multivariate analysis using principal component analysis (PCA) showed a cultivar-specific methylation during stress and that methylation changes between cultivars are much higher than that of within a cultivar. Higher methylation to demethylation in Bolani (30.06 vs. 22.12%) compared to that of cultivar Sistan (23.21 vs. 30.15%) indicated more demethylation did not induce tolerance responses in Sistan. Sequencing differentially methylated fragments along with qRT-PCR analysis showed the efficient role of various DNA fragments, including demethylated fragments such as phosphoenol pyruvate carboxylase (PEPC), beta-glucosidase (BGlu), glycosyltransferase (GT), glutathione S-transferase (GST) and lysine demethylase (LSD) genes and methylated fragments like ubiquitin E2 enzyme genes in the development of drought tolerance. These results suggested the specific roles of DNA methylation in development of drought tolerance in wheat landrace.

Tolerance responses in wheat landrace Bolani are related to enhanced metabolic adjustments under drought stress.

Physio-biochemical adaptations of wheat landraces may have great importance in their growth, survival and yield under drought stress. Here, we evaluated the effects of drought stress on some defense systems of wheat cultivar "Sistan" (drought-sensitive) and landrace "Bolani" (drought-tolerant). Under drought stress, Bolani plants showed lower increases in hydrogen peroxide content compared to Sistan ones, which was accompanied with significant decrease in malondialdehyde and electrolyte leakage indices. Increasing the transcript levels and activity of enzymatic and non-enzymatic antioxidants along with phenylpropanoid metabolites improved relative tolerance to drought-induced oxidative stress, particularly in Bolani plants, results which may be confirmed by a significant decrease in the damage indices. In the phenylpropanoid pathway, the biosynthetic pathway of total phenol, flavonoids and anthocyanins was more active than lignin-biosynthetic pathway, which could early respond to drought stress. These results may be confirmed by their negative significant correlations with damage indices as well as a non-significant correlation of lignin with most enzymatic and non-enzymatic antioxidants in plants. Lower decrease of chlorophyll (Chl) and carotenoid contents in Bolani plants compared to Sistan ones indicated the relative stability of photosynthetic pigments under drought stress. Our results suggested that integrating metabolic pathways could coordinately alleviate oxidative stress that can lead to introducing suitable genetic sources for drought tolerance.