EMBRYO SAC DEVELOPMENT IS AFFECTED IN PETUNIA-INFLATA PLANTS TRANSFORMED WITH AN ANTISENSE GENE ENCODING THE EXTRACELLULAR DOMAIN OF RECEPTOR KINASE PRK1

In a previous study of the function of a pollen-expressed receptor kin ase of Petunia inflata, PRK1, it was found that transgenic plants carr ying an antisense-PRK1 gene were unable to transmit the transgene thro ugh either the male or, unexpectedly, the female. In this report, the nature of this female phenotype was studied using one of the transgeni c plants, ASRK-13. Electron and light microscopic examination of the e mbryo sac and seed development of ASRK-13 and a wild-type plant reveal ed that embryo sac development of approximately half of the ovules of ASRK-13 was abnormal. The development of the affected embryo sacs was arrested at the late stages of megagametogenesis. The majority of the affected embryo sacs completed three rounds of mitosis normally, but f ailed to progress through the maturation stages when cell expansion, n uclear migration, and differentiation take place. The remaining small number of abnormal embryo sacs were arrested at either the four- or ei ght-nucleate stages. The ovules containing the defective embryo sacs a pparently failed to be fertilized, resulting in degeneration of half o f the seeds produced by ASRK-13. RNA gel blot analysis suggests that t he PRK1 gene is expressed in the ovary, albeit at a much lower level t han in the anther. The possibility that the antisense PRK1 gene is res ponsible for the abnormal embryo sac development is discussed.