ARS | Publication request: The regulatory role of reversible phosphorylation in the chlorophyll degradation pathway

Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2011
Publication Date: August 6, 2011
Citation: Hall, P.K., Ort, D.R. 2011. The regulatory role of reversible phosphorylation in the chlorophyll degradation pathway [abstract]. American Society of Plant Biologists. Paper No. P02046.

Technical Abstract: Senescence represents the final stage of plant development and is characterized by several processes including the systematic degradation of the photosynthetic apparatus and chlorophyll molecules inside chloroplasts. Normally, chlorophyll is catabolized to colorless compounds through a series of enzyme-mediated steps, however, various environmental stresses encountered during the growing period have the potential to impair chlorophyll catabolism so that residual chlorophyll remains in organs and tissues after senescence is complete. Post-senescence chlorophyll retention is commonly seen in mature canola (Brassica napus) seeds that have been exposed to freezing temperatures early during seed development. Studies have shown that the major enzyme in chlorophyll catabolism impaired by this low temperature exposure is pheophorbide a oxygenase (PaO). A strong suppression of PaO activity – which correlates with an increase in the ratio of phosphorylated to dephosphorylated PaO - is observed in canola receiving a freeze treatment, suggesting that PaO may be controlled posttranslationally. Using site-directed mutagenesis at putative phosphorylation sites, we have created phospho- and dephospho-mimic mutants in Arabidopsis to explore the possible role of reversible phosphorylation in PaO activation. We hypothesize that enzyme activity and extent of chlorophyll degradation will differ between the two mutants and wildtype control, supporting the notion that PaO activity is primarily regulated by reversible phosphorylation.