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Identification and characterization of a pectin acetylesterase from the seed coat of common bean (Phaseolus vulgaris)

Palmer J, Pajak A, Marsolais F (2017) Identification and characterization of a pectin acetylesterase from the seed coat of common bean (Phaseolus vulgaris). Oral presentation. 2017 Biennial Bean Improvement Cooperative Meeting. East Lansing, MI, October 29-November 1

Abstract

Common bean is rich in dietary fibre, a major component of which is pectin present in the seed coat. Pectin is produced as an esterified polymer in the Golgi apparatus, which can be de-esterified after it is secreted. The enzyme pectin acetylesterase participates in this process. De-esterification can change the structural properties of the cell wall. Esterification decreases calcium binding and gelation of pectin. A gene designated PAE1 was characterized which encodes a major pectin acetylesterase in the seed coat. This gene is differentially expressed at all stages of seed development between germplasm lines SARC1 and SMARC1N-PN1, with transcript levels higher in SMARC1N-PN1 by 5- to 16-fold according to microarray data. The transcript was found to accumulate specifically in the seed coat, and the difference in expression between genotypes was confirmed by quantitative RT-PCR. Protein accumulation was observed in seed coat extracts of SARC1 and SMARC1N-PN1 by Western blot, with levels higher in SMARC1N-PN1 by approximately 2-fold. Initial velocity of pectin acetylesterase in seed coat extracts was higher by approximately 3-fold in SMARC1N-PN1. The acetate content of purified pectin from seed coats was 2.8 fold higher in SARC1 than SMARC1N-PN1. The difference in pectin acetylesterase expression is associated with an insertion of 150 base pair insertion in the promoter of SARC1. SMARC1N-PN1 was found to have a decreased seed water uptake and germination as compared with SARC1, particularly in older seeds.

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