In vivo Expression of a Cicer arietinum β-galactosidase in Potato Tubers Leads to a Reduction of the Galactan Side-chains in Cell Wall Pectin

Abstract

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.