European researchers led by Michael Holdsworth from University of Nottingham conducted a study on improving the flood tolerance of barley plants. This was done by adapting their previous study in Arabidpsis thaliana that leads to the discovery of plants' mechanism to sense low oxygen levels during flood conditions. The researchers look at the N-end rule pathway which is responsible for plants' response to low oxygen during flooding. This pathway works by controlling the stability of group VII ethylene response factor (ERFVII) and transcription factors as dictated by the oxidation status of amino terminal (Nt)-cysteine (Cys).

In the case of barley, their study reveals that ERFVII are N-end rule substrate that also functions as a homeostatic sensor of hypoxia. Genetic manipulation was conducted to reduce expression of this pathway. Transgenic RNAi barley plant having a reduced expression of N-end rule pathway N-recognin E3 ligase PROTEOLYSIS6 (HvPRT6) and a transgenic barley plant without HvPRT6, Barley Targeting Induced Local Lesions IN Genomes (TILLING) lines were subject to flooding conditions and comparison between the transgenic barley plants was conducted.

Results show that HvPRT6 RNAi plants gain an increased tolerance to flooding as indicated by its sustained growth and yield, greater chlorophyll retention and delayed leaf senescence under continuous dark condition. Both the HvPRT6 RNAi plant and TILLING lines had an increase in the expression of hypoxia-related genes and production of mature seed phenotypes. These findings show the importance of the N-end rule pathway in plant breeding to improve plants' tolerance to flooding.

Full details of the study can be read at Wiley Online Library.

Figure 5. Reduced HvPRT6 expression delays leaf senescence. (a) Photographs of leaf sections from RNAi lines and nontransgenic controls following treatment with darkness on liquid media for 6 days. (b) Quantification of colour change in leaf sections following transformation of images of leaf segments from RGB to HSV colour space. The 50% confidence regions are shown as ellipses (thick for null lines and thin for RNAi lines).