Ectopic expression of a rice transcription factor, Mybleu, enhances tolerance of transgenic plants of Carrizo citrange to low oxygen stress

Oxygen deficit, which occurs in flooded or poorly drained soils, can limit plant growth and development. Low-oxygen environmental conditions also limit the distribution of many woody plants, such as citrus trees, which are considered flood-sensitive crops, although tolerance to this stress varies among genotypes and rootstocks. In this study, the rice transcription factor Mybleu was inserted into the pGA470 plant cloning vector and transferred into the epicotyl explants of the Carrizo citrange rootstock (Citrus sinensis x Poncirus trifoliata) using Agrobacterium tumefaciens-mediated transformation. The transgenic lines were confirmed for the presence and expression of the transgene, and physiological, biochemical and molecular parameters were evaluated for adaptation to hypoxic and anoxic stress conditions. The ectopic expression of Mybleu increased tolerance to oxygen deprivation in the transgenic lines, contributing to increased viability under this stress condition. This improved tolerance correlates with, and may depend on, the induction of genes and the activation of enzymes from various fermentation and carbohydrate metabolic pathways, antioxidant systems and nonsymbiotic haemoglobin-nitric oxide homeostasis mechanisms. Together, our data suggest a key role for Mybleu in coordinating the multifaceted plant response to low oxygen stress and the conservation of Mybleu-regulated pathways among species.