Functional analysis of genes for tyrosine catabolism that may be involved in annual and perennial differentiation of rice

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Although glutathione S-transferases (GSTs) are family of enzyme involved in the detoxification of per-oxidized materials in cells, Zeta class of GST (GSTZ) is reported as the maleylacetoacetate isomerase (MAAI) which detoxify homogentisate, intermediate in the catabolic pathway of tyrosine and phenylalanine. The genome of rice contains two copies of gene encoding GSTZ. Two GSTZ genes of O. sativa, OsGSTZ1 and OsGSTZ2, lies in tandem-arranged orientation. Upstream OsGSTZ1 gene constitutively expresses whereas downstream OsGSTZ2 gene is inducible by stresses. We analyzed the expression of GSTZ gene in African cultivated species O. glaberrima and wild species O. longistaminata by using RT-PCR. The result showed that both GSTZ1 and GSTZ2 genes expressed in O. longistaminata, whereas only cDNA fragment of downstream GSTZ2 was detected in 0. glaberrima. Thus, the genomic sequence of GSTZ1 locus of O. glaberrima was determined by PCR genomic walking. The sequence comparison between O. sativa and O. glaberrima revealed that genomic sequence upstream from the eighth intron of OgGSTZ1 gene was highly homologous, in inverted orientation, to a BAC clone, apart over 1-Mb from OsGSTZ1 gene in O. sativa. This result suggested that OgGSTZ1 gene was disrupted by huge rearrangement or inversion. The genetic alteration was shared with several lines of O. glaberrima and its ancestral wild species O. barthii. The lost of OgGSTZ1 gene in O. glaberrima is interesting which is mainly expressed 12-fold higher than OsGSTZ2 in O. sativa and some different characters exist between O. sativa and O. glaberrima, like seed yield and annual/perennial habitat that might be related with the translocation of nitrogen metabolites from leaves to seeds. GSTZ1 gene is being introduced into O. glaberrima to convert annual to perennial habitat.