Differences in expression between two seed lectin alleles obtained from normal and lectin-deficient beans are maintained in transgenic tobacco

Abstract

Using Agrobacterium-mediated transformation, two genes for phytohemagglutinin-L (PHA-L), the lectin seed protein of the common bean Phaseolus vulgaris, were stably integrated into the tobacco genome. The two alleles for PHA-L, dlec2 and pdlec2, were obtained from a normal cultivar (Greensleeves) and a lectin-deficient cultivar (Pinto) respectively. In the bean embryos, the expression of dlec2 is 30 times greater than the expression of pdlec2. In the dlec2-transformed tobacco, PHA-L accumulated specifically in the seeds at the same stages as the tobacco seed storage proteins and was degraded after germination. PHA-L was found in the embryo, and at a 5-7 times lower concentration in the endosperm tissue of the mature tobacco seeds. No PHA could be detected in other parts of the plants. We conclude that the signals for temporal and spatial regulation of the dlec2 gene are present in the DNA fragment used for transformation. Transformation with the second PHA-L allele pdlec2 from the cultivar Pinto caused the accumulation of about 50 times less PHA-L in tobacco seeds when compared to dlec2. We conclude from analyzing the 5' sequences of dlec2 and Pdlec2 that the low expression phenotype of the Pdlec2 allele could be due to the absence or mutation of a cis-acting element carried by the dlec2 fragment.