The GT92 (predicted galactosyltransferase) gene family, previously known as the DUF23 family, has about 60 representatives in the C. elegans genome, few of which have any known function. Mutants in one GT92 gene,
subs-4 (Y47D3B.1) were recovered as SUppressors of Bacterial Sensitivity, exploiting the observation that
srf-2 and
srf-5 mutants are efficiently killed by the surface pathogen Leucobacter Verde1, unlike wildtype worms (Hodgkin et al. 2013). In srf(+) backgrounds, however, the
subs-4 mutants exhibited embryonic lethality. The lethal mutant phenotype was rescued by a 7 kb genomic transgene, indicating that a 3 kb upstream region is sufficient for normal
subs-4 expression. Some but not all multicopy
subs-4(+) transgene arrays were found to provide partial maternal rescue to
subs-4 mutant progeny, so that these survived as arrested larvae rather than dying as late embryos. These arrested larvae exhibited massive vacuolation and greatly increased permeability to dyes, indicating that
subs-4 is essential for osmotic integrity and permeability barriers. Reporter transgene constructs using
subs-4p::GFP showed that the gene is expressed in all somatic tissues. Surprisingly, the GFP expressed in these transgenic lines was strongly localized to mitochondria. Inspection of the predicted 3'UTR for Y47D3B.1 revealed an unpredicted additional in-frame exon, which may be mitochondrially targeted. Other GT92 proteins in C. elegans include GALT-1, which has known galactosyltransferase activity and confers sensitivity to a fungal toxin (Titz et al. 2009), BAH-1 (Drace et al. 2009), BAH-2, BAH-4 and SRF-2. We found that mutations in all of the corresponding genes affected adhesion to worms by Leucobacter Verde1 and to biofilm formation on worms by Yersinia pseudotuberculosis (the Bah, Biofilm Absent on Head, phenotype), implying that all of these proteins modify surface coat properties. Interactions between different GT92 mutants were investigated, because
subs-4 lethality is suppressed in
subs-4;
srf-2 double mutants. The other GT92 mutants (
galt-1,
bah-1,
bah-2,
bah-4) did not suppress
subs-4 embryonic lethality but other double mutant effects were discovered, indicating complex interactions among GT family members.