CONSERVED EXPRESSION OF A TASSELSEED2 HOMOLOG IN THE TAPETUM OF THE DIOECIOUS SILENE LATIFOLIA AND ARABIDOPSIS-THALIANA

To investigate the genetics of male sex determination and stamen devel opment in the dioecious plant Silene latifolia (white campion), male-s pecific transcripts were isolated from developing flowers by cDNA subt raction. One of the cDNAs identified, STA1 had high DNA and amino acid sequence homology to the male sex determining gene of Zea mays (maize ), TASSELSEED2. Both genes are expressed in male and not in female flo wers, However, they do not share the same expression pattern. The TASS ELSEED2 gene product is expressed in the gynoecium primordia of male m aize flowers where it is necessary for pistil abortion. STA? is not ex pressed in the gynoecium primordia of male white campion and therefore its gene product cannot perform the same function in sex determinatio n that TASSELSEED2 performs in maize. STA I is expressed in tapetal ce lls of white campion male flowers and of white campion hermaphroditic mutants. A homologous gene is also expressed in the tapetum of hermaph roditic Silene species. Tapetal expression of a homologous gene (named ATA1) was also found in Arabidopsis thaliana. The similarity in prima ry sequence and expression pattern of STA? and ATA1 indicate that thes e genes have a conserved role in tapetum development.