Abstract
Sexual plant reproduction involves the deposition of pollen on top of the stigma, followed by pollen germination, pollen tube growth within the pistil and leading to delivery of the sperm cells to the embryo sac for fertilisation. One approach to study genes essential for this unique intercellular processes involves the screening of Arabidopsis T-DNA tagged populations and searching for lines with a non-Mendelian segregation of marker genes, due to reduced T-DNA transmission. The main focus of this thesis is the genetic, molecular and cellular characterization of a male gametophytic mutant, found in such a mutant population by segregation distortion analysis. The hemizygous mutant line TJ995 showed a severe defect in male T-DNA transmission efficiency, with only 2% of the mutant pollen tubes being able to achieve fertilization. No defect through the female gametophyte was found. TJ995 showed bursting of the mutant pollen during pollen germination and pollen tube growth in vitro, and the mutant was called bursting pollen (bup/+). Molecular and genetic studies showed that the male gametophytic defect of bup/+ was due to the T-DNA insertional mutation of gene At5g04480 (BURSTING POLLEN). BUP encodes a golgi-resident type II transmembrane protein showing similarity with family 1 glycosyl transferases, and appears to be strongly conserved through evolution. BUP and its Arabidopsis homologue BUP like (BPL) are both constitutively expressed at low levels in pollen and in vegetative tissues, but appear to have different functions within the male gametophyte. We hypothesize that BUP is involved in the synthesis of pectin present in the intine layer of the pollen (tube) wall and in sporophytic cell walls, and as such is important for the pollen wall and cell wall plasticity and strength.
