|Kim, Sang Ic|
|ANDAYA, VIRGILIO - California Rice Experiment Station|
Submitted to: Biochemical Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2011
Publication Date: 4/15/2011
Citation: Kim, S., Andaya, V., Tai, T. 2011. Cold sensitivity in rice (Oryza sativa L.) is strongly correlated with a naturally occurring I99V mutation in the multifunctional glutathione transferase isoenzyme GSTZ2. Biochemical Journal. 435:373-380.
Interpretive Summary: Seedling cold tolerance in rice is important for good crop stand establishment and uniform maturation, both of which affect productivity. The qCTS12 locus contains a gene (or genes) that provide a major degree of protection against chilling injury in rice seedlings. In this study, we have undertaken molecular genetic and biochemical experiments to analyze two potential genes responsible for this tolerance, OsGSTZ1 and OsGSTZ2. Our results indicated that the OsGSTZ2 gene from the cold tolerant California rice variety M-202 encodes an enzyme that differs by two amino acids from the cold sensitive variety IR50. The enzyme from the cold tolerant M-202 is significantly more active than the enzyme from the sensitive IR50 because of one of those amino acid differences. A DNA marker developed to detect this specific difference in OsGSZT2 was used to test a diverse collection of rice varieties and showed a good correlation with visual assessment of seedling cold tolerance. This small difference in the OsGSTZ2 gene and the resulting change in the activity of the OsGSTZ2 enzyme may explain in part the differences in sensitivity to chilling injury between rice varieties from temperate versus tropical climates.
Technical Abstract: GSTZs (zeta class glutathione transferases) belong to a highly conserved subfamily of soluble GSTs found in species ranging from fungi and plants to animals. GSTZ is identical to MAAI (maleylacetoacetate isomerase), which functions in tyrosine catabolism by catalyzing the isomerization of MAA (maleylacetoacetate) to FAA (fumarylacetoacetate). As tyrosine metabolism in plants differs from animals, the significance of GSTZ/MAAI is unclear. In rice (Oryza sativa L.), a major QTL for seedling cold tolerance has been fine mapped to a region containing the genes OsGSTZ1 and OsGSZT2. Sequencing of tolerant (ssp. japonica cv. M-202) and sensitive (ssp. indica cv. IR50) cultivars revealed two SNP (single nucleotide polymorphisms) in OsGSTZ2 that result in amino acid differences (I99V and N184I). Recombinant OsGSTZ2 containing the Val99 residue found in IR50 had significantly reduced activity on MAA and DCA (dichloroacetic acid), but the Ile184 residue had no effect. The distribution of the SNP (c.295A>G) among various rice accessions indicates a significant association with chilling sensitivity in rice seedlings. These results show that naturally occurring OsGSTZ2 isoforms differ in their enzymatic properties which may contribute to the differential response to chilling stress generally exhibited by the two major rice subspecies.