Abscisic acid -insensitive mutants and AFLP mapping in the fern Ceratopteris richardii
The sex of the gametophyte of the homosporous fern Ceratopteris richardii (Brongn.) is determined by the pheromone antheridiogen (ACE). Wild-type spores germinating in the absence of the pheromone will develop into hermaphroditic gametophytes, whereas spores continuously exposed to the pheromone will develop as males. The hormone abscisic acid (ABA) is able to inhibit the antheridiogen response, causing wild-type gametophytes to develop as small hermaphroditic gametophytes with reduced cell size in the presence ACE. The abscisic acid-resistant (abr) mutants abr1 and abr2 have been previously characterized. Twelve additional mutants were isolated in this study. Five of these mutants were characterized, along with abr1 and abr2. The abr mutants develop as males in the presence of ACE and 10 μM ABA. Linkage analysis shows that the seven mutations comprise at least four loci: abr1, 4, and 5; abr2; abr3 and 6; and abr7. The abr mutants of Ceratopteris do not have impaired stomatal regulation, cold tolerance, germination, or altered response to sugars, phenotypes associated with ABA resistance in Arabidopsis. Tests of epistasis suggest a role for ABA and the ABR genes in inhibiting antheridium formation by inhibiting the repression of the TRA genes by ACE and the HER genes in the developing gametophyte. In a separate study, the feasibility of using amplified fragment length polymorphisms (AFLP) to construct a framework map of the Ceratopteris genome for use in cloning genes of Ceratopteris was examined. 150 polymorphic markers were detected between the Hnn and N8 strains of Ceratopteris. Chi-square analysis revealed segregation distortion in 75% of the markers scored in 71 individuals from one mapping population, and in 80% of the markers scored in 118 individuals from a second mapping population, indicating that AFLP markers can not be used to construct a map at this time. Two of eight her loci tested for segregation in her (Hnn) × N8 hybrids also exhibited segregation distortion, indicating that the observed segregation distortion is not limited to AFLP markers. Chromosome squashes of F1 spore mother cells indicate a possible meiotic cause for the observed distortion. ^
Major Professor: Jo Ann Banks, Purdue University.
Biology, Botany|Biology, Genetics