Characterization of two cDNAs encoding glutathione S-transferases in rice and induction of their transcripts by the herbicide safener fenclorim

The safener fenclorim (4,6-dichloro-2-phenyl-pyrimidine) induces glutathione S-transferases (GSTs; EC 2.5.18) in rice (Oryza sativa L. cv. Lemont), including those with activity toward pretilachlor [2-chloro-2',6'-diethyl-N-(2-propoxyethyl)acetamide] and this is associated with increased tolerance to this herbicide. In this study. we report on the isolation and characterization of two partial cDNA clones encoding GSTs in rice. The two cDNA clones were isolated by using GST-specific degenerate primers and the RT-PCR (reverse transcriptase-polymerase chain reaction) technique from control (unsafened) and fenclorim-treated (safened) rice roots, respectively. Sequence analyses demonstrated that the two cDNAs share 60% amino acid sequence identity and 62% nucleotide sequence identity, appearing to represent two different rice GSTs (RGST I and II). Southern blot analysis with the tao clones confirmed the presence of at least three GST genes in the rice genome, Northern blotting with the two clones as probes showed that the GST gene(s) are constitutively expressed in roots of unsafened rice seedlings. Treatment with the safener fenclorim induced the expression of the rice GST gene(s). The fenclorim-mediated induction of mRNA expression coincided with a concomitant induction of total GST activity toward pretilachlor in roots of fenclorim-safened rice. Phylogenetic analysis based on the amino acid sequence alignment of the tno rice cDNAs with sequences of other plant GSTs shelved that RGST I seems to be more closely related to wheat GSTs, while RGST II is more closely related to the maize GST I and IV isozymes.