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To identify genes with essential roles in male gametophytic development, including postpollination (progamic) events, we have undertaken a genetic screen based on segregation ratio distortion of a transposon-borne kanamycin-resistance marker. In a population of 3359 Arabidopsis Ds transposon insertion lines, we identified 20 mutants with stably reduced segregation ratios arising from reduced gametophytic transmission. All 20 mutants showed strict cosegregation of Ds and the reduced gametophytic transmission phenotype. Among these, 10 mutants affected both male and female transmission and 10 mutants showed male-specific transmission defects. Four male and female (ungud) mutants and 1 male-specific mutant showed cellular defects in microspores and/or in developing pollen. The 6 remaining ungud mutants and 9 male-specific (seth) mutants affected pollen functions during progamic development. In vitro and in vivo analyses are reported for 5 seth mutants. seth6 completely blocked pollen germination, while seth7 strongly reduced pollen germination efficiency and tube growth. In contrast, seth8, seth9, or seth10 pollen showed reduced competitive ability that was linked to slower rates of pollen tube growth. Gene sequences disrupted in seth insertions suggest essential functions for putative SETH proteins in diverse processes including protein anchoring, cell wall biosynthesis, signaling, and metabolism., (Copyright 2004 Genetics Society of America)

Glycosylphosphatidylinositol (GPI) anchoring provides an alternative to transmembrane domains for anchoring proteins to the cell surface in eukaryotes. GPI anchors are synthesized in the endoplasmic reticulum via the sequential addition of monosaccharides, fatty acids, and phosphoethanolamines to phosphatidylinositol. Deficiencies in GPI biosynthesis lead to embryonic lethality in animals and to conditional lethality in eukaryotic microbes by blocking cell growth, cell division, or morphogenesis. We report the genetic and phenotypic analysis of insertional mutations disrupting SETH1 and SETH2, which encode Arabidopsis homologs of two conserved proteins involved in the first step of the GPI biosynthetic pathway. seth1 and seth2 mutations specifically block male transmission and pollen function. This results from reduced pollen germination and tube growth, which are associated with abnormal callose deposition. This finding suggests an essential role for GPI anchor biosynthesis in pollen tube wall deposition or metabolism. Using transcriptomic and proteomic approaches, we identified 47 genes that encode potential GPI-anchored proteins that are expressed in pollen and demonstrated that at least 11 of these proteins are associated with pollen membranes by GPI anchoring. Many of the identified candidate proteins are homologous with proteins involved in cell wall synthesis and remodeling or intercellular signaling and adhesion, and they likely play important roles in the establishment and maintenance of polarized pollen tube growth.