TIP1
Palmitoyation in plants
Palmitoylation, more correctly known as S-acylation, is a protein modification common to all eukaryotes that allows the reversible association of proteins with membranes.
Arabidopsis thaliana or Thale cress is the best studied and understood model plant system and has a fully sequenced and comprehensively annotated genome. Like animals and fungi, plants utilise S-acylation and the other hydrophobic lipid modifications myristoylation, farnesylation and geranylgeranylation to enable protein association with membranes. Where plants differ is in how they are used.
Prenylation
Geranylgeranylation is used extensively in plants while farnesylation is used much less than would be expected when compared to other systems. Interestingly loss of either or both modifications is not lethal although plants do appear different to wild type (Running et al., 2004,) . This is in marked contrast to fungi and animals where the loss of geranylgeranylation is much more serious and frequently lethal.
Myristoylation
Arabidopsis contains two N-myristoyltransferase genes and 0.8% of Arabidopsis proteins are predicted to be myristoylated compared to 0.5% for humans and 0.3% for fungi underlining the relative importance of myristoylation to plant growth.
S-acylation
23 DHHC S-acyl transferase genes are present in the Arabidopsis genome. Currently there are very few known S-acylated proteins in plants although it would appear that, given the number of DHHC proteins present, regulation of S-acylation in plants is likely to be an important and complex process.
Loss of the TIP1 S-acyl transferase in tip1-2 mutant plants leads to reduction in cell size, plant size fertility and growth polarity. The loss of growth polarity is best demonstrated by the shortening and branching of root hairs and the erratic and growth of pollen tubes that frequently change thier direction of growth.
S-acyl transferases S-acyl transferases were first identified in yeast by Nick Davis' lab when they showed that AKR1 is able to attach palmitate groups to Yeast Casein Kinase 2 (YCK2, (Roth et al., 2002) TIP1 is the only one of the 23 Arabidopsis S-acyl transferases to contain an aditional recognised domain in addition to the DHHC domain. TIP1 contains 6 ankyrin repeats at the N terminus and is similar to AKR1 from budding yeast and HIP14 from Humans and these proteins form a distinct subset of S-acyl transferases.
