Pectin Methylesterase

Arabidopsis (Arabidopsis thaliana) QUARTET (QRT) genes are required for pollen separation during normal floral development. In qrt mutants, the four products of microsporogenesis remain fused and pollen grains are released as tetrads. In Arabidopsis, tetrad analysis in qrt mutants has been used to map all five centromeres, easily distinguish sporophytic from gametophytic mutations, and accurately assess crossover interference. Using a combination of forward and reverse genetics, we have identified the gene responsible for the qrt1 phenotype. Annotation predicts that QRT1 encodes a pectin methylesterase (PME), and enzymatic assays of QRT1 expressed in Escherichia coli indicate that QRT1 has PME activity. Promoter and transcription analysis demonstrate QRT1 is expressed in anther tissues shortly after meiosis is complete. Unexpectedly, the QRT1 promoter is also active in a variety of developmentally unrelated tissues, including developing guard cells, the hypocotyl-root transition zone, areas of lateral root emergence, and floral nectaries. PMEs constitute a large gene family in Arabidopsis, are involved in cell wall loosening, and have been implicated in various aspects of floral development and pollen tube elongation. The identification of QRT1 as a PME contributes to our understanding of pollen development and may help to provide valuable genetic tools in other plant species.

Several cell-wall degrading enzymes have been studied and their action involved in the softening concomitant with ripening of various fruits. However, studies pertaining to pectin methylesterase (PME) that catalyzes the demethylesterification of cell wall polygalacturonans have been very limited especially in fruit tissue. The present study covers the biochemical characterization of pectin methylesterase from Musa acuminata in context to delayed ripening phenomenon, principally dealing withidentification of a PME gene, namely, PME 1 from Grand Naineveriety of banana. The expression of this gene was well correlated with the ripening. After Ethylene treatment the expression of PME1 gene was peaked on day 3 while in control fruit, the progression of ripening was rather slow. The GA content was observed to augment significantly during the course of ripening of banana fruit. The overall data obtained provide new insights into correlation of the expression of PME1 with increased PME1 with increased PME activity as well as pectin content.