Expression of class 1 phytoglobin (HvPgb1) promotes waterlogging tolerance responses in barley (Hordeum vulgare L.)

Abstract

Barley (Hordeum vulgare L.) is the most susceptible cereal species to excess moisture stress. Waterlogging-induced hypoxia causes major physiological changes that disrupt the photosynthetic machinery of seedlings. The signaling molecule nitric oxide (NO) regulates numerous metabolic processes but increases to toxic levels during hypoxia. Phytoglobin1 (Pgb1) functions as a NO-scavenging hemeprotein that influences hypoxic stress responses such as ethylene-mediated adaptations and nitrate use. This study demonstrated that overexpression of HvPgb1 maintains photosynthetic rate in barley during waterlogging, but also confirms previously reported decreases in physiological performance during normoxic (control) conditions. Foliar ethylene was found to decrease in waterlogged wild type (WT) but remain unchanged in the HvPgb1-overexpressing line [HvPgb1(OE)]. It is proposed that ACC from the hypoxic root mobilizes to the shoot, where it induces HvPgb1 activity and nitrate generation. Foliar nitrate was measured as well and showed a significant increase in leaves of waterlogged HvPgb1(OE) plants, while remaining unchanged in waterlogged WT leaves. These changes were associated to a putative increased in the levels of polyamines. Finally, HvPgb1 expression was measured from a group of selected waterlogging-tolerant and susceptible genotypes. A sharp increase in gene expression was seen in the leaves of waterlogged tolerant genotypes, thus positioning HvPgb1 expression as a potential molecular marker for waterlogging tolerance in barley.