Arabidopsis HIT1, a putative homolog of yeast tethering protein Vps53p, is required for pollen tube elongation

The Arabidopsis HIT1 gene encodes a protein that is homologous to the yeast tethering factor Vps53p, which is involved in retrograde vesicle trafficking from the endosome to the trans-Golgi network. Although the ethyl methanesulfonate mutagenized hit1-1 allele can be maintained homozygously, T-DNA insertional hit1-2 and hit1-3 mutants can only be isolated as hemizygous lines. No heterozygous progeny were produced in outcrosses to wild-type plants using pollen from either hit1-2 or hit1-3 heterozygotes. The reciprocal cross using pollen from wild-type plants on either hit1-2 or hit1-3 mutants produced heterozygous and wild-type progeny. In reproductive tissues, HIT1 promoter-driven GUS activity was detected only in mature pollen and elongated pollen tubes. In vitro pollen germination further showed that only half the pollen grains from hit1-2 and hit1-3 heterozygote plants produced normal pollen tubes. In contrast, the pollen tube length of pollen grains from the hit1-1 mutant was reduced compared to that of the wild type. These results suggest that HIT1 may govern a vesicle trafficking event that is required for pollen tube tip growth during male gametogenesis and that disruption of HIT1 results in male specific transmission defect. Moreover, while the hit1-1 mutant is partially functional leading to reduced pollen tube length, hit1-2 and hit1-3 are total-loss-of-function alleles.