The cDNA clone (CanBGal-3) encoding a cell wall pectin-degrading β-galactosidase (βIII-Gal) from Cicer arietinum L. cv. Castellana has been identified. The identification was carried out by comparing the deduced amino acid sequences of several isolated chickpea β-galactosidase clones with the purified βIII-Gal protein sequence. The expression pattern of the gene corresponding to CanBGal-3 was in concordance with the fluctuations of the enzyme βIII-Gal in different seedling organs, being specific to elongating organs such as epicotyls and roots. Transformation of Solanum tuberosum plants with the chickpea CanBGal-3 clone indicated that the β-galactosidase encoded by this clone is a pectin-degrading enzyme. The authors propose an important role for chickpea βIII-Gal in pectin degradation in cell walls of vegetative organs such as epicotyls and roots. The degradation of galactan carried out by this enzyme may determine structural changes and affect cell wall porosity. It is suggested that the increase in the size of cell wall pores could permit access of other cell wall-modifying enzymes to their substrate.

We report the generation of Solanum tuberosum transformants expressing Cicer arietinum βIII-Gal. βIII-Gal is a β-galactosidase able to degrade cell wall pectins during cell wall loosening that occurs prior to cell elongation. cDNA corresponding to the gene encoding this protein was identified among several chickpea β-galactosidase cDNAs, and named CanBGal-3. CanBGal-3 cDNA was expressed in potato under the control of the granule-bound starch synthase promoter. Three βIII-Gal transformants with varying levels of expression were chosen for further analysis. The transgenic plants displayed no significant altered phenotype compared to the wild type. However, β-galactanase and β-galactosidase activities were increased in the transgenic tuber cell walls and this affected the potato tuber pectins. A reduction in the galactosyl content of up to 50% compared to the wild type was observed in the most extreme transformant, indicating a reduction of 1,4-β-galactan side-chains, as revealed by analysis with LM5 specific antibodies. Our results confirm the notion that the pectin-degrading activity of chickpea βIII-Gal reported in vitro also occurs in vivo and in other plants, and confirm the involvement of βIII-Gal in the cell wall autolysis process. An increase in the homogalacturonan content of transgenic tuber cell walls was also observed by Fourier transform infrared spectroscopy (FTIR) analysis.