Pectin acetylesterase 8 influences pectin acetylation in the seed coat, seed imbibition, and dormancy in common bean (Phaseolus vulgaris L.)

Abstract The results of a prior transcript profiling study identified a large difference in transcript accumulation of a pectin acetylesterase gene, designated as PAE8, in two genetically related lines of common bean (Phaseolus vulgaris). The results of reverse transcription‐quantitative PCR experiments confirmed this difference and revealed that the gene is expressed specifically in the seed coat of developing seeds. Genomic sequence data identified a non‐functional allele, due to a five‐base pair insertion resulting in a frameshift and premature stop codon. The non‐functional pae8 allele was associated with a lack of detectable protein as determined by Western blot. PAE8 accounted for approximately 65% of total pectin acetylesterase activity in the developing seed coat. Lack of functional PAE8 resulted in an approximately 2.5‐fold increase in acetylation of soluble pectin in the mature seed coat. The presence of a non‐functional pae8 allele was associated with an increased rate of water absorption by the seed and increased percentage of germination in aged seeds. The data suggest that the decreased acetylation of pectin leads to enhanced interaction with Ca2+, contributing to water impermeability.