Poster: Oxidative stress

Abs # 70: Enhanced catalytic activity of phospholipid hydroperoxide glutathione peroxidase interferes with plant regeneration

Presenter:	Eshdat, Yuval , vhyuval@agri.gov.il
Authors	Faltin, Zehava  (A)   Perl, Avi  (A)   Velcheva, Margarita  (B)   Tsapovetsky, Marina  (A)   Holland, Doron  (A)   Roeckel-Drevet, Patricia  (C)   Handa, Avtar K (D)   Abu-Abied, Muhamad  (A)   Friedman-Einat, Miriam  (A)   Eshdat, Yuval  (A)
Affiliations:	(A): Agricultural Research Organization, Volcani Center, Israel (B): Agricultural University, Plovdiv, Bulgaria (C): Universite Blaise Pascal, Clermont Ferrand, France (D): Purdue University, West Lafayette, IN, USA
Web Site:	http://www.agri. gov.il

PHGPx, a unique plant glutathione peroxidase-like protein, is over-expressed under conditions which mediate oxidative stress. To study its unknown biological role and its potential to confer stress resistance in plants, we tried to obtain constitutive over-expression of citrus-PHGPx in transgenic plants. Such attempts to regenerate plants following agrobacterium-mediated transformation in tomato, potato and tobacco, have failed. On the other hand, efficient PHGPx expression was obtained in tobacco and potato cell lines and leaves when cultured, following transformation, on callus induction non-regenerative media only. Moreover, we did succeed in obtaining transgenic tobacco plants that over-express citrus-PHGPx merely by using a strong inducible promoter, and transgenic Arabidopsis plants by employing in-planta transformation thus eliminating the in vitro step. These results imply that PHGPx over-expression hampers regeneration of the transgenic plants. To establish whether enhanced PHGPx catalytic activity in the transformed cells interferes with the plant regeneration and possibly differentiation, site-directed mutagenesis of the presumed catalytic residue (Cys41) of citrus-PHGPx into Ser41 was done. Agrobacterium-mediated transformation utilizing this mutated PHGPx-cDNA yielded transgenic tobacco plants which constitutively over-express citrus-PHGPx devoid of catalytic activity. Thus, enhanced non-regulated enzymatic activity of PHGPx abolishes regeneration of plants. Our findings strongly imply that PHGPx participates in mediating proper balance of oxy-radicals, which controls metabolic signaling regulation that is essential for plant development and critical for differentiation-related events during the regeneration stage, rather than cell division.