Molecular Analysis of a Family of Arabidopsis Genes Related to Galacturonosyltransferases

We are studying a Galacturonosyltransferase-Like (GATL) gene family in Arabidopsis (Arabidopsis thaliana) that was identified bioinformatically as being closely related to a group of 15 genes (Galacturonosyltransferase1 [GAUT1] to -15), one of which (GAUT1) has been shown to encode a functional galacturonosyltransferase. Here, we describe the phylogeny, gene structure, evolutionary history, genomic organization, protein topology, and expression pattern of this gene family in Arabidopsis. Expression studies (reverse transcription-polymerase chain reaction) demonstrate that all 10 AtGATL genes are transcribed, albeit to varying degrees, in Arabidopsis tissues. Promoter::β-glucuronidase expression studies show that individual AtGATL gene family members have both overlapping and unique expression patterns. Nine of the 10 AtGATL genes are expressed in all major plant organs, although not always in all cell types of those organs. AtGATL4 expression appears to be confined to pollen grains. Most of the AtGATL genes are expressed strongly in vascular tissue in both the stem and hypocotyl. Subcellular localization studies of several GATL proteins using yellow fluorescent protein tagging provide evidence supporting the Golgi localization of these proteins. Plants carrying T-DNA insertions in three AtGATL genes (atgatl3, atgatl6, and atgatl9) have reduced amounts of GalA in their stem cell walls. The xylose content increased in atgatl3 and atgatl6 stem walls. Glycome profiling of cell wall fractions from these mutants using a toolkit of diverse plant glycan-directed monoclonal antibodies showed that the mutations affect both pectins and hemicelluloses and alter overall wall structure, as indicated by altered epitope extractability patterns. The data presented suggest that the AtGATL genes encode proteins involved in cell wall biosynthesis, but their precise roles in wall biosynthesis remain to be substantiated.