Regulation of expression of a ubiquitous tomato pectin methylesterase gene (pmeu1) during plant growth and development

Pectin methylesterase (PME), an ubiquitous enzyme in plants, has been suggested to play many roles in plant growth and development. We have characterized a pectin methylesterase gene (pmeu1) that is expressed in all plant tissues. I have isolated and sequenced a genomic DNA fragment containing the pmeu1 gene and its 5′ and 3 ′ flanking regions to evaluate the biological function of this pectin methylesterase isozyme. Computer analysis of the 5′-flanking region shows the presence of several known cis-acting elements including G-box, abscisic acid responsive element and light regulated elements. I have generated transgenic tomato and tobacco plants expressing a reporter gene under the control of different lengths of pmeu1 5′-flanking regions. The histochemical localization of β-glucuronidase (GUS) in these transgenic plants showed that the patterns of β-glucuronidase expression under the pmeu1 promoter are similar in homologous tomato and heterologous tobacco in all tissues, except ovary in tomato and immature seeds in tobacco. The levels of β-glucuronidase under the pmeu1 promoter is roots \u3e stem \u3e leaf. The –267 bp of pmeu1 5′-flanking region are sufficient for pmeu1 expression, but at least two enhancer elements are present upstream of this promoter region. One of these enhancer elements seems to play a role in expression in undifferentiated and differentiated tissues. Characterization of pmeu1 expression during growth cycle of cell suspension cultures made from transgenic tobacco plants expressing β-glucuronidase under the pmeu1 promoter suggests a role of this enzyme in cell expansion. However, up to 10-fold increase in PME activity, due to over-expression of pmeu1 under the control of CaMV 35S, does not modify the growth attributes of transgenic tobacco cells in the liquid medium. Growth and development of transgenic tobacco plants over-expressing pmeu1 under the CaMV 35S were examined. Phenotype of pmeu1 over-expressing tobacco plants is similar to the wild type plants but seed set is impaired in pmeu1 overexpressing plants due to the lack of pollen germination/tube elongation. Although the final height of the transgenic plants overexpressing pectin methylesterase was similar to the wild type, during the early growth period pmeu1 overexpressing plants attained height faster than the wild-type plants. Further characterization of transgenic plants, especially role of pectin chemistry in biophysical properties of cell wall, ion accumulation, and other physiological parameters, will help understanding the role of pectin methylesterase and pectin chemistry in plant growth and development