Submitted to: Physiologia Plantarum
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/9/2003
Publication Date: 1/1/2003
Citation: MUHITCH, M.J., LIANG, H., SOLLENBERGER, K.G. TRANSFORMATION EFFICIENCIES AND EXPRESSION PATTERNS OF A SERIES OF TRUNCATED GS1-2 PROMOTER/GUS TRANSGENES IN MAIZE. PHYSIOLOGIA PLANTARUM. 2003. v. 118. p. 346-351. Interpretive Summary: Developing corn seeds receive nutrients through their pedicels, the neck-like structure that attaches them to the cob. Pedicels are also important ports of entry into the seed for various disease organisms. Previously, we have shown that a unique form of glutamine synthetase (GS), an important enzyme in nitrogen interconversions, is found in abundance within this region. We have cloned the pedicel GS gene and shown that it can be used to cause pedicel-specific gene expression and protein accumulation. In this report, we present the results of experiments where the gene was progressively shortened from one end to see the effects on its function. These experiments add knowledge necessary for the design of a genetic tool for expressing disease resistance and other beneficial genes in the pedicel region of the kernels. This offers great potential for improvements in corn kernel quality in terms of increased disease resistance as well as other agronomic traits.
Technical Abstract: One isoform of maize glutamine synthetase, encoded by GS1-2, is localized exclusively within the maternal tissues of the developing kernel. In this report, a series GS1-2 promoter/GUS reporter transgenes, progressively truncated from the 5' end of the promoter, were evaluated for transformation efficiency and their ability to drive tissue-specific gene expression in transgenic maize. All of the transgenes were efficiently incorporated into the maize genome, but inefficiently expressed in bialophos-resistant calli. Removal of 270 bases from the 5' end of the full length promoter, to 394 base pairs upstream of the putative transcription start site, resulted in the loss of kernel tissue specificity. Also, maize plants transformed with the full length promoter construct that exhibited GUS activity in resistant calli were less efficient at retaining GUS expression in regenerated plants than were those plant lines transformed with truncated versions of the transgene. Evidence is presented that gene silencing, rather than gene instability, accounts for the inefficient expression of GUS in transformants and, moreover, that there is within the same upstream segment of the GS1-2 promoter that regulates tissue specific expression, an element that increases silencing of the GS1-2 gene in trans.