The conserved plant sterility gene HAP2 functions after attachment of fusogenic membranes in Chlamydomonas and Plasmodium gametes

Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Genes & Development (Impact Factor: 10.8). 05/2008; 22(8):1051-68. DOI: 10.1101/gad.1656508
Source: PubMed


The cellular and molecular mechanisms that underlie species-specific membrane fusion between male and female gametes remain largely unknown. Here, by use of gene discovery methods in the green alga Chlamydomonas, gene disruption in the rodent malaria parasite Plasmodium berghei, and distinctive features of fertilization in both organisms, we report discovery of a mechanism that accounts for a conserved protein required for gamete fusion. A screen for fusion mutants in Chlamydomonas identified a homolog of HAP2, an Arabidopsis sterility gene. Moreover, HAP2 disruption in Plasmodium blocked fertilization and thereby mosquito transmission of malaria. HAP2 localizes at the fusion site of Chlamydomonas minus gametes, yet Chlamydomonas minus and Plasmodium hap2 male gametes retain the ability, using other, species-limited proteins, to form tight prefusion membrane attachments with their respective gamete partners. Membrane dye experiments show that HAP2 is essential for membrane merger. Thus, in two distantly related eukaryotes, species-limited proteins govern access to a conserved protein essential for membrane fusion.

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    • "For example, DUO1 is a MYB transcription factor that is essential to male 311 germline transcription and identity, with specific expression in generative and sperm cells of 312 Arabidopsis (Rotman et al., 2005; Brownfield et al., 2009a; Borg et al., 2011). The highly conserved 313 GCS1/HAP2 gene encoding a secreted membrane protein is essential for fertilization in a myriad of 314 other eukaryotes as well (Mori et al., 2006; von Besser et al., 2006; Liu et al., 2008). Additional male 315 gamete-selective genes have been identified and characterized in lily and Arabidopsis (Engel et al., 2005; 316 Okada et al., 2005a; Okada et al., 2005b; Brownfield et al., 2009a Brownfield et al., , 2009b). "
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    • "We have also found a small number of microgametes with associated DNA and some 9 + 0 axonemes (Table 1) but it is still difficult to conceive how these immotile gametes can fertilize. One hypothesis is if gametes are by chance physically touching, membrane fusion of gametes of opposite sex mediated by fusogenic proteins like HAP2 (Liu et al., 2008) – which is present in Δsas6 (Fig. S3D) – can prevail over lack of motility. "
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