Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2009
Publication Date: 4/30/2009
Publication URL: http://hdl.handle.net/10113/33380
Citation: Booij, I.S., Edelman, M., Mattoo, A.K. 2009. Nitric oxide (N0) donor-mediated inhibition of phosphorylation shows that light-mediated degradation of photosystem II D1 protein and phosphorylation are not tightly linked. Planta. 229:1347-1352. Interpretive Summary: Nitrogen, an essential nutrient for plant growth and development, is oxidized to toxic forms such as nitric oxides during its utilization. One such molecule is nitric oxide (NO), which can be both beneficial and toxic to plants and animals. NO is also known to be a bioactive molecule that has been suggested to be a new hormone because it is found to be a part of the plant signaling process in response to abiotic and biotic stresses. Very little is known about the mechanisms by which NO regulates plant processes. In plants, excessive concentrations of NO were previously shown to negatively impact photosynthetic apparatus. We show here, for the first time, that NO targets phosphorylation event of a key membrane protein D1 in the photosynthetic organelle, chloroplasts. Using the inhibitory effect of NO, we further demonstrate that phosphorylation of D1 protein is unlinked with its well known rapid degradation process. Because D1 is a key protein involved in photochemistry that ultimately enhances crop productivity, excessive production of NO in plants may negatively impact crop productivity. These findings should be of interest to scientists in the areas of agronomy, physiology, biochemistry, molecular biology, protein science, agriculture and horticulture.
Technical Abstract: A major outcome of the photochemistry during oxygenic photosynthesis is the rapid turn over of the D1 protein in the light compared to the other proteins of the photosystem II (PS II) reaction center. D1 is a major factor of PS II instability and its replacement a primary event of the PS II repair cycle. D1 also undergoes redox-dependent phosphorylation prior to its degradation. Although it has been suggested that phosphorylation downregulates D1 metabolism, reversible D1 phosphorylation was reported not to be essential for PS II repair in Arabidopsis. Thus, the involvement of phosphorylation in D1 degradation is controversial. We show here that nitric oxide (NO) donors target and inhibit in vivo phosphorylation of PS II proteins in Spirodela without affecting de novo protein synthesis. Applying NO donors, we show that protein phosphorylation and D1 degradation are not linked. Likewise, a known inhibitor of dephosphorylation, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), is shown not to inhibit D1 degradation. Thus, reversible phosphorylation of D1 is independent of D1 degradation in the intact plant.