Isolation of expressed gene sequences from the stigma of Brassica oleracea
Molecular characterisation of the stigma and style in the Cruciferae has concentrated exclusively on the components of the SI system, and other members of their sequence families, while neglecting other sequences involved in tissue development and compatible pollination. To address this imbalance work has been carried out to isolate expressed gene sequences from the stigma of Brassica oleracea. cDNA clones were isolated from a cDNA library and characterised together with two clones isolated previously. Four out of eleven clones represented previously isolated S-gene and S-related gene sequences which have been extensively studied by other workers. One other sequence that could be positively identified encodes a putative glycine-rich cell wall protein which is expressed strongly in the stigma and more weakly in the style and petal, suggesting that it plays a specific role in the former. Of the other isolated clones, two cross-hybridise with closely related transcripts that are stress- induced in vegetative tissue. This allows parallels to be drawn with the Solanaceae, in which proteins, normally induced by stress, are also expressed in healthy carpels. However, the Brassica species differ from these in that they are expressed in all floral whorls. Neither stress-induced clone can be positively identified although their encoded proteins share homology with the major latex protein of poppy and two bacterial protein sequences. Of the remaining four sequences, two were enriched in stigmas, but contained insufficient sequence data to allow identification. The third sequence was expressed throughout the mature plant, though expression was higher in floral tissue, while expression of the fourth could not be determined. From these sequences no information concerning the molecular basis stigma development and function can be deduced. Therefore other approaches to studying this tissue are discussed.