Characterization of a xylem AGP gene expressed in pine, poplar and Arabidopsis

Arabinogalactan-proteins (AGPs) are proteins involved in the development of plants that are frequently associated with the extracellular matrix. PtX14A9 is an AGP encoding gene cloned from a loblolly pine xylem cDNA library. It has very high expression in differentiating xylem and very low or non-detectable expression in other tissues. Several genes that are similar to PtX14A9 were cloned from poplar and Arabidopsis thialiana or identified in the DNA databases. A short conserved amino acid motif was found in cell surface related genes from different plant species as well as in other non-plant species. In order to understand the functions of these 14A9-like genes, I used antisense and overexpression approaches in poplar and Arabidopsis. Although most of the transformants had a normal phenotype and no detectable structural changes, two lines of the antisense At156 plants were very abnormal. The most severe antisense mutants, 156Eyellow plants, have retarded overall growth on media, irregularly shaped pale or translucent leaves and abnormal shoots. They did not elongate or flower on the artificial media and did not survive in soil. Northern blot and quantitative RT-PCR confirmed the high level of antisense transcripts in the mutants. These results may indicate that 14A9-like genes are critical for normal plant development.