FERTILIZATION-INDEPENDENT SEED DEVELOPMENT IN ARABIDOPSIS-THALIANA

We report mutants in Arabidopsis thaliana (fertilization-independent s eed:fis) in which certain processes of seed development are uncoupled from the double fertilization event that occurs after pollination. The se mutants were isolated as ethyl methanesulfonate-induced pseudo-reve rtants of the pistillata phenotype. Although the pistillata (pi) mutan t has short siliques devoid of seed, the fis mutants in the pi backgro und have long siliques containing developing seeds, even though the fl owers remain free of pollen. The three fis mutations map to loci on th ree different chromosomes. In fis1 and fis2 seeds, the autonomous endo sperm nuclei are diploid and the endosperm develops to the point of ce llularization; the partially developed seeds then atrophy. In these tw o mutants, proembryos are formed in a low proportion of seeds and do n ot develop beyond the globular stage. When FIS/fis plants are pollinat ed by pollen from FIS/FIS plants, approximate to 50% of the resulting seeds contain fully developed embryos; these seeds germinate and form viable seedlings (FIS/FIS). The other 50% of seeds shrivel and do not germinate; they contain embryos arrested at the torpedo stage (FIS/fis ). In normal sexual reproduction, the products of the FIS genes are li kely to play important regulatory roles in the development of seed aft er fertilization.