EVALUATION OF GENES TO REDUCE SEED SIZE IN ARABIDOPSIS AND TOBACCO AND THEIR APPLICATION TO CITRUS

Seedlessness is a highly desirable characteristic in fresh fruit. Mark etability of a fruit as seedless does not require complete absence of seeds as long as the seed structures are imperceptible during consumpt ion. Chimaeric genes comprised of soybean beta-conglycinin seed storag e protein gene promoters linked to the bacterial RNase gene, Barnase, were tested for their efficacy to cause seed death and decrease seed s ize in tobacco and Arabidopsis. These species were used because they u ndergo two distinct seed developmental pathways and produce albuminous and exalbuminous seeds, respectively. In both species, the death of e mbryo and endosperm tissues occurred, resulting in a dominant seed let hal phenotype with segregation distortion. Reduction in seed size was only observed in Arabidopsis seeds and the phenotype resembled that of stenospermocarpic seeds in grape. Some transformants of both species were male-sterile and this correlated with the expression of the gene in anthers indicating that expression of the gene is not strictly seed -specific. The promoters also direct expression of a linked GUS gene t o Citrus embryos of various developmental stages, and Citrus forms exa lbuminous seeds, therefore, the Barnase constructions may be useful in eliciting a reduction in seed size of around 75% of the seeds found i n the fruit. This may be sufficient to warrant marketing as 'less seed y' if trials in the cultivar of interest indicate that the smaller see ds are less detectable to the consumer.