How plants sense low oxygen

The recent identification of the oxygen-sensing mechanism in plants is a breakthrough in plant physiology. The presence of a conserved N-terminal motif on some ethylene responsive factors (ERFs), targets the protein for post-translational modifications finally leading to degradation under normoxia and thus providing a mechanism for sensing the presence of oxygen. The stabilization of the N-terminus under low oxygen activates these ERFs, which regulate low oxygen core genes that enable plants to tolerate abiotic stress such as flooding. Additional mechanisms that signal low-oxygen probably also exist, and the production of reactive oxygen species (ROS) has been observed under low oxygen, suggesting that ROS might be part of the network involved in plant acclimation. Here, we review the most recent findings related to oxygen sensing

Flooding tolerance in plants

Global warming is associated with an increase in flooding events, making many ecosystems worldwide vulnerable to submergence. Water submersion can severely affect crop production, since it drastically reduces oxygen availability necessary for plants' respiration, thus survival. Plants tolerant to flooding evolved morphological, physiological and biochemical adaptations to oxygen deficiency. Recently, considerable progress has been made in terms of understanding the molecular aspects governing these responses. However, the upstream stress-sensing mechanism of oxygen shortage has not yet been fully understood and many of the systems described in bacteria, fungi and animals have been excluded for plants. Many studies on oxygen deprivation stress have focused on rice (Oryza sativa), since it is one of the crops better adapted to a flooded environment. Beside being able to germinate under submergence, rice varieties display different mechanisms for a successful survival. Agronomically, the study of rice strategies to survive flooding in ecotypes adapted to extreme environments shows big potential in the context of climate change and the worldwide increasing need for food

ROS signaling as common element in low oxygen and heat stresses

The activation of the oxidative metabolism in plants under low oxygen conditions has prompted controversial views. The presence of a ROS component in the transcriptome in response to low oxygen has been observed and an overlap with heat stress has been proved. It has been also demonstrated that ROS are produced during both anoxia and heat, but the site of their production remain contentious. Membrane NADPH oxidase and mitochondrial electron transport flow have been indicated as possible ROS generation systems. Both anoxia and heat have been shown to induce the transcription of Heat Shock Factors (HSFs) and Heat Shock Proteins (HSPs), among which HSFA2 and some of its targets. HSFA2 over-expressing plant has been shown to be more tolerant to anoxia, while the knockout hsfa2 lose the capability of wild type plants to cross-acclimate to anoxia through mild heat pre-treatment. The production of ROS seems to be an integral part of the anoxia and heat response, where HSFs likely play a central role in activating the HSP pathway. This mechanism is suggested to result in enhanced plant tolerance to both anoxia and heat

Ethylene influences in vitro regeneration frequency in the FR13A rice harbouring the SUB1A gene

Many studies have examined the effects of ethylene on in vitro plant growth and development, often with controversial results. Ethylene accumulates in culture vessels due to both the release from the tissues and the physical entrapment due to the need for closed containers. This hormone has several effects on plant regeneration, depending on the plant species and even the cultivar. A prerequisite for ethylene use for in vitro culture is thus to formulate a specific protocol for the genotype of interest. In rice, ethylene is a key regulator of adaptation strategies to low oxygen environments. In particular, the SUBMERGENCE1A (SUB1A) gene, when present, drives the acclimation response which when activated by ethylene produced by submerged plants leads to adaptation through reduced plant growth and ethanolic fermentation enhancement. This gene is restricted to a limited number of rice for which a very specific response to ethylene is expected, whatever the source. This paper reports the regeneration differences between a SUB1A rice landrace (indica-aus, FR13A) and a non-SUB1A variety (japonica, Nipponbare). Our results suggest that regeneration protocols with exogenous ethylene precursors supply are required for the FR13A rice harbouring the SUB1A gene to overcome the problem of low regeneration efficiency

Reactive oxygen species-driven transcription in Arabidopsis under oxygen deprivation

Reactive oxygen species (ROS) play an important role as triggers of gene expression during biotic and abiotic stresses, among which is low oxygen (O2). Previous studies have shown that ROS regulation under low O2 is driven by a RHO-like GTPase that allows tight control of hydrogen peroxide (H2O2) production. H2O2 is thought to regulate the expression of heat shock proteins, in a mechanism that is common to both O2 deprivation and to heat stress. In this work, we used publicly available Arabidopsis (Arabidopsis thaliana) microarray datasets related to ROS and O2 deprivation to define transcriptome convergence pattern. Our results show that although Arabidopsis response to anoxic and hypoxic treatments share a common core of genes related to the anaerobic metabolism, they differ in terms of ROS-related gene response. We propose that H2O2 production under O2 deprivation is a trait present in a very early phase of anoxia, and that ROS are needed for the regulation of a set of genes belonging to the heat shock protein and ROS-mediated groups. This mechanism, likely not regulated via the N-end rule pathway for O2 sensing, is probably mediated by a NADPH oxidase and it is involved in plant tolerance to the stress

Molecular analysis of a sunflower gene encoding an homologous of the B subunit of a CAAT binding factor

A genomic DNA fragment containing the complete LEAFY COTYLEDON1-LIKE (HaL1L) gene was retrieved by chromosome walking. Its sequence was confirmed and elongated by screening a sunflower genomic DNA BAC Library. HaL1L, whose cDNA had already been sequenced and characterized, encodes a NF-YB subunit of a CCAAT box-binding factor (NF-Y) involved in the early stages of zygotic and somatic embryogenesis in the Helianthus genus. In the HaL1L 50-flanking region, elements specific to a putative TATA-box promoter and two ‘‘CG isles’’ were identified. An investigation of the methylation status of these CG rich DNA regions showed that differentially methylated cytosines were recognizable in the DNA of embryos on the fifth day after pollination in comparison to leaf DNA suggesting that during plant development epigenetic regulation of HaL1L transcription was achieved by methylating cytosine residues. We also searched the HaL1L nucleotide sequence for cis-regulatory elements able to interact with other transcription factors (TFs) involved in the HaL1L regulation. Of the elements identified, one of the most intriguing is WUSATA, the target sequence for the WUSCHEL (WUS) TF, which may be part of a complex regulation network controlling embryo development. In this article, we show that the WUSATA target site, located in the intron of HaL1L, is able to bind the TF WUS. Interestingly, we found auxin and abscisic acid responsive motifs in the HaL1L promoter region suggesting that this gene may additionally by under hormonal control. Finally, the presence of a cytoplasmic polyadenylation signal downstream to the coding region indicates that this gene may also be controlled at the translation level by a temporarily making the pre-synthesized HaL1L mRNA unavailable for protein synthesis