Characterization of Tagetes patula cDNA clones obtained by differential screening in relation to thiophene biosynthesis

In an attempt to isolate genes involved in thiophene metabolism, a cDNA library was constructed from poly(A) super(+) RNA of a thiophene-producing root culture of Tagetes patula and differentially screened against a cDNA probe prepared from poly(A) super(+) RNA of leaves, which are low in thiophenes. Five cDNA clones were selected for expression and sequence analysis. Two clones, containing previously unknown sequences, revealed the accumulation of gene transcripts in roots and hypocotyls but not in leaves of both Tagetes species. Since thiophenes predominantly accumulated in roots and hypocotyls, it is concluded that with respect to transcript distribution, the genes corresponding to these two clones are expressed as expected for genes of thiophene biosynthesis. However, in roots, the steady-state levels of the transcripts detected by both clones did not reflect the differences in thiophene content and thiophene synthesizing capacity, indicating that the corresponding genes are not involved in rate-limiting steps of the secondary pathway. Three cDNA clones showing homology to pathogenesis-related proteins of the Betvl-type revealed the accumulation of transcripts exclusively in roots of T. patula and T. erecta.