Expressing foreign genes in the pistil: a comparison of S-RNase constructs in different Nicotiana backgrounds

Transgenic plant experiments have great potential for extending our understanding of the role of specific genes in controlling pollination. Often, the intent of such experiments is to over-express a gene and test for effects on pollination. We have examined the efficiency of six different S-RNase constructs in Nicotiana species and hybrids. Each construct contained the coding region, intron, and downstream sequences from the Nicotiana alata SA2-RNase gene. Among the six expression constructs, two utilized the cauliflower mosaic virus (CaMV) 35S promoter with duplicated enhancer, and four utilized promoters from genes expressed primarily in pistils. The latter included promoters from the tomato Chi2;1 and 9612 genes, a promoter from the N. alata SA2-RNase gene, and a promoter from the Brassica SLG-13 gene. Some or all of the constructs were tested in N. tabacum, N. plumbaginifolia, N. plumbaginifolia × SI N. alata SC10SC10 hybrids, N. langsdorffii, and N. langsdorffii × SC N. alata hybrids. Stylar specific RNase activities and SA2-RNase transcript levels were determined in transformed plants. Constructs including the tomato Chi2;1 gene promoter or the Brassica SLG-13 promoter provided the highest levels of SA2-RNase expression. Transgene expression patterns were tightly regulated, the highest level of expression was observed in post-anthesis styles. Expression levels of the SA2-RNase transgenes was dependent on the genetic background of the host. Higher levels of SA2-RNase expression were observed in N. plumbaginifolia × SC N. alata hybrids than in N. plumbaginifolia.