Identification of QTL Related to ROS Formation under Hypoxia and Their Association with Waterlogging and Salt Tolerance in Barley

Abstract

Waterlogging is a serious environmental problem that limits agricultural production in low-lying rainfed areas around the world. The major constraint that plants face in a waterlogging situation is the reduced oxygen availability. Accordingly, all previous efforts of plant breeders focused on traits providing adequate supply of oxygen to roots under waterlogging conditions, such as enhanced aerenchyma formation or reduced radial oxygen loss. However, reduced oxygen concentration in waterlogged soils also leads to oxygen deficiency in plant tissues, resulting in an excessive accumulation of reactive oxygen species (ROS) in plants. To the best of our knowledge, this trait has never been targeted in breeding programs and thus represents an untapped resource for improving plant performance in waterlogged soils. To identify the quantitative trait loci (QTL) for ROS tolerance in barley, 187 double haploid (DH) lines from a cross between TX9425 and Naso Nijo were screened for superoxide anion (O2•−) and hydrogen peroxide (H2O2)—two major ROS species accumulated under hypoxia stress. We show that quantifying ROS content after 48 h hypoxia could be a fast and reliable approach for the selection of waterlogging tolerant barley genotypes. The same QTL on chromosome 2H was identified for both O2•− (QSO.TxNn.2H) and H2O2 (QHP.TxNn.2H) contents. This QTL was located at the same position as the QTL for the overall waterlogging and salt tolerance reported in previous studies, explaining 23% and 24% of the phenotypic variation for O2•− and H2O2 contents, respectively. The analysis showed a causal association between ROS production and both waterlogging and salt stress tolerance. Waterlogging and salinity are two major abiotic factors affecting crop production around the globe and frequently occur together. The markers associated with this QTL could potentially be used in future breeding programs to improve waterlogging and salinity tolerance.

Genome-Wide Analysis of Gene Expression Provides New Insights into Waterlogging Responses in Barley (Hordeum vulgare L.)

“…All of these suggest that there might not be a clear, general correlation between waterlogging stress tolerance and the activity of major enzymatic antioxidants, but a more genotype-dependent one. When performing GO enrichment analysis on up and down-regulated genes, ROS related GO terms were down-regulated in Deder2 at 72 and 120 h. For example, the discrepancy between our results and those reported by Gill et al [33] that screened the barley roots for ROS production under hypoxia stress could be due to the treatment applied (hypoxia solution-0.2% agar vs. waterlogging) but most likely is due to the timing of the measurements, 48 h vs. 72 and 120 h. Previously, Zhu et al [69] has shown that the activities of SOD, CAT, and POD in grapevine leaves under waterlogging stress increased substantially compared to the control but began declining after 24 h (CAT) and 96 h (SOD and POD). A similar trend was observed in Deder2 for those three POD up-regulated genes identified in our study where they were more expressed at 72 h (2.56, 2.00, and 2.21 logFC) compared to 120 h (2.15, 1.48, and 1.47 logFC).…”

“…ROS-scavenging enzymes and antioxidants are induced to protect the plants against ROS, which is accumulated under waterlogging conditions creating oxidative stress [60]. They play a critical role, in the plant cells, in the survival under waterlogging of many plants, such as winter wheat [61], maize [45], barley [33], and cucumber [62]. The top 11 Biological Process GO terms for all DEGs were related to ROS catabolic processes, including hydrogen peroxide metabolic process, detoxification, oxidation-reduction process, response to oxidative stress, etc.…”

“…In recent years, a large number of quantitative trait loci (QTLs) for waterlogging tolerance affecting important traits have been identified in barley, such as root aerenchyma formation [29,30], root membrane potential [31], root porosity [30,32], and ROS formation [33]. Despite the numerous QTL studies conducted to date on waterlogging in barley, the responsible genes underlying the response to waterlogging remain unknown [34].…”

The State of the Art in Modeling Waterlogging Impacts on Plants: What Do We Know and What Do We Need to Know

“…Another pathway through which contemporary models could account for effects of waterlogging is oxidative stress damage. This is because exposure of plants to hypoxia or anoxia conditions causes oxidative stress, which affects plant growth due to the production of superoxide radicals, hydroxyl radicals, and hydrogen peroxide (Gill et al, 2019; Mittler et al, 2004). ROS accumulation also results in a significant disturbance to plant ionic homeostasis, directly affecting activity of various cation (Gill et al, 2019; Shabala et al, 2014) and anion channels (Pottosin et al, 2018).…”

Exogenous salicylic acid ameliorates waterlogging stress damages and improves photosynthetic efficiency and antioxidative defense system in waxy corn

“…Plants minimize oxidative stress by producing enzymatic and nonenzymatic antioxidants. The antioxidant enzyme system, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), alleviate and scavenge waterlogging-induced ROS production from the plant cells (Gill et al 2019, Jia et al 2019, Wang et al 2019b. SOD catalyzes the conversion of O2 •into O2 and H2O2, while H2O2 is effectively scavenged by POD and CAT.…”