Expansin Genes Expressed Differentially in Peduncle Elongation of Near-Isogenic Wheat Rht Lines

Abstract

The introduction of reduced height (Rht) genes Rht-B1b and Rht-D1b led to impressive increases in wheat (Triticum aestivum L.) yields during the Green Revolution. In the present study, the dynamic elongation of peduncle in a set of near-isogenic lines (NILs) carrying different Rht alleles (Rht-B1b, Rht-D1b, Rht-B1c, Rht-D1b+Rht-B1b, and Rht-D1b+Rht-B1c) were investigated. The reduction of the final length of peduncle in NILs was dependent mainly on the elongation rate, which was reduced by Rht genes, during rapid elongation phase. Resin sections showed that Rht genes strongly reduced the cell extension in peduncle. The expression of expansin genes, which mediate cell wall loosening and leading to cell expansion, were analysed by using real-time quantitative PCR (qPCR). Among the 23 possible wheat expansin genes, 17 were expressed in the peduncle. The spatial distribution of expression was further analysed for five expansins that showed high expression levels in the peduncles of Rht lines. Compared to wild type plants, the incorporation of Rht-D1b allele decreased about 37 and 80% of the expression levels of ExpA7 and ExpA3 in elongation zone, respectively. The presence Rht-B1c dwarfing genes, however, produced 53% reduction in the expression level of ExpA7, and seriously decreased about 70% of ExpB9 expression. Although the expression levels of five genes exhibited variability among the lines, an expansin gene, ExpB2, showed its expression level highly associated with the cell elongation rate in peduncle of different Rht lines.

Keywords

• expansin
• peduncle
• gene expression
• dwarfing gene