Poster: Oxidative Stress

Abs # 143: Increase sensitivity to oxidative stress in transgenic Arabidopsis plants with low levels of plastid Methionine Sulfoxide Reductase

Presenter:	Romero, Hernan M, hmr116@psu.edu
Authors	Romero, Hernan M (A) (D)  Jensen, Philip  (B)   Pell, Eva J (B)   Tien, Ming  (C)
Affiliations:	(A): Intercollege Graduate Program in Plant Physiology. The Pennsylvania State University (B): Department of Plant Pathology. The Pennsylvania State University (C): Department of Biochemistry and Molecular Biology. The Pennsylvania State University (D): Department of Biology. Universidad Nacional de Colombia
Web Site:	http://www.lsc.psu.edu/plantphys.html

Proteins are major targets of oxidative stress (OS). Damage to amino acid residues can lead to rapid protein turnover via proteolysis. Met residues are the most susceptible to OS leading to formation of the sulfoxides (MetOH). MetOH can be reduced back to Met by the enzyme methionine sulfoxide reductase (PMSR), with the recovery of protein function. There are five genes that encode PMSR in Arabidopsis. One gene product is localized to the chloroplast (PSMR-1), the others to the cytoplasm. PMSR-1 seems to be involved in repairing proteins damaged by OS during photosynthesis. The cytoplasmic forms might have alternative functions. To study the role of PMSR in OS protection we constructed Arabidopsis antisense plants with reduced expression of PMSR-1 and tested their susceptibility to different OS conditions. Transgenic lines with lower levels of PMSR-1, relative to the wild type, were obtained and subjected to either 10 µM methyl viologen (MV), high light (HL), or 350 ppb ozone (O3). Chlorophyll a fluorescence (FLUO), photosynthetic activity (A), PMSR activity, and total peptidyl MetOH were measured in plants under the different treatments. Plants with reduced amount of PMSR-1 were more susceptible to MV and HL, but not to O3. A was reduced in response to the different treatments. With O3, the reduction was similar in all the lines, however with MV and HL, A was proportional to the amount of PMSR-1 in the chloroplast. FLUO was also affected in the antisense lines exposed to MV and HL, but not in those treated with O3. We conclude that PMSR-1 is indeed an important enzyme in the response of plants to OS in the chloroplast. Since it's likely that O3 imposes OS mainly in the cytosol, reduced levels of PMSR-1 do not seem to affect the response of plants to this stress.