Flooding events have increased significantly because of global climate change, in which rising water levels decrease oxygen levels for plants. When on top of a growing population, flooding leads to severe crop loss, feeding the world gets critical. Scientific research so far has mostly focused on how plants respond when flooded, but less studies focus on recovery after flooding. Therefore Elaine Yeung compared two Arabidopsis thaliana ecotypes with different recovery rates.
PhD Elaine Yeung
Molecular mechanisms mediating post-submergence recovery in Arabidopsis thaliana
Lp2-6 (naturally found in Lipovec, Czech Republic) was defined as a flooding tolerant plant that recovered faster, and Bay-0 as a flooding intolerant plant with slower recovery (found in Bayreuth, Germany). Lp2-6 retains more green leaves after a flooding event and grows new leaves faster, resulting in more seed yield.
By using a Ribosome-sequencing technique, Yeung managed to explain the differences in recovery rates between Lp2-6 and Bay-0 on the molecular level. Lp2-6 and Bay-0 turn out to have contrasting gene expression for processes related to photosynthesis, light responses, antioxidant capacity, dehydration, and senescence. Yeung also identified hormones signalling these biological processes.
When flooding is over, plants must adapt to a new environment with high levels of sunlight and oxygen compared to under water. This causes reactive oxygen species (ROS) to form in the plant, which are very damaging molecules that hinder photosynthesis. Plants also cannot take up water through the roots, causing leaves to undergo senescence and desiccation stress.
ROS formes very quickly after the plant is removed from under water and is highest in Bay-0 at 3 hours of recovery. Lp2-6 has lower ROS formation during recovery because of higher antioxidant levels. ROS was found to be produced in the form of hydrogen peroxide through the gene Respiratory Burst Oxidase Homologue D (RbohD), which was highly induced in Bay-0. However, a minimal level of ROS signalling was required for recovery.
Post-submergence recovery also induces dehydration and senescence, since leaves can't take up water from damaged roots. Bay-0 gets more yellowing leaves and lower water content because stomata are not able to close. The plant hormone abscisic acid (ABA), which normally closes the stomata, instead increases levels of the gene Senescence Associated Gene 113 (SAG113). This keeps the stomata open, so more water is lost. Early senescence in Bay-0 occurs also because of higher ORE1/NAC Domain Containing Protein 6 (NAC6) and Chloroplast Vesiculation (CV) gene expression.
In Lp2-6, induction of GATA, Nitrate-inducible Carbon-metabolism involved (GNC) and GNC-like/Cytokinin-responsive GATA Factor 1 (GNL/CGA1) helped the stomata close and delayed senescence. Yeung concludes that controlling ROS and stomatal aperture are therefore critical for improving recovery.