Virus-induced silencing of a plant cellulose synthase gene

Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infect ed with one group of cDNAs had much shorter internode lengths, small leaves , and a "dwarf" phenotype. Consistent with a loss of cell wall cellulose, a bnormally large and in many cases spherical cells ballooned from the unders urfaces of leaves, particularly in regions adjacent to vascular tissues. Li nkage analyses of wall polysaccharides prepared from infected leaves reveal ed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected pl ants. The decrease in cellulose content in cell walls was offset by an incr ease in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from similar to 50 to similar to 33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellul ose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellu lose synthase genes.