A putative pectin acetylesterase gene family in Arabidopsis thaliana

Pectin is a class of acidic plant cell wall polysaccharides that comprises a major fraction of the Type I primary cell wall, typical of dicotyledonous species. Galacturonic acid residues of pectin can be acetylated at the O-2 and O-3 positions. The enzyme pectin acetylesterase (PAE) can hydrolyze acetyl esters in homogalacturonan regions of pectin. Decreasing the degree of acetylation of pectin gels in vitro alters their physical properties. In vivo acetylesterase activity in Arabidopsis root cell walls was detected with an apparent optimum pH of 6.5. The degree of acetylation of two-week-old Arabidopsis shoot and root cell walls were 10% and 6% respectively. Eleven putative genes have been identified in the Arabidopsis genome with sequence similarity to known PAE encoding genes. Atpae3 x Atpae6 double mutant line had 70% and 83% of wild type root tissue of fresh weight and dry weight respectively. This significant difference could be the result of structural changes of cell wall of the double mutant line, since no difference was observed of root length or number of lateral roots between the wild type and Atpae3 x Atpae6 double mutant line. FTIR analysis on PGA with two different degrees of acetylation showed a wave number peak of 1747 cm-1.