Male flower-specific expression of genes for polygalacturonase, pectin methylesterase and beta-1,3-glucanase in a dioecious willow (Salix gilgiana Seemen).

We isolated cDNA clones (pSgPG1 through pSgPG4, pSgPME1 and pSgGN1) for the polygalacturonases (PGs), pectin methylesterase (PME) and beta-1,3-glucanase (GN) that are expressed specifically in male flowers of the dioecious willow (Salix gilgiana Seemen). The structural characteristics of the deduced proteins, designated SgPGs, SgPME1 and SgGN1, respectively, suggest that these enzymes function in pollens or anthers. The four SgPGs were more than 91.9% homologous to one another at the amino acid level, indicating that their genes are members of a single family. Although the expression of the SgPGs, SgPME1 and SgGN1 was specific to male catkins (inflorescences), these genes were found in the genomes of both male and female plants. The expression of the transcripts of SgPGs, SgPME1 and SgGN1 was regulated developmentally in male reproductive organs. Maximal expression of SgPGs and SgPME1 was detected when male flowers were fully open and mature, while maximal expression of SgGN1 occurred at an earlier time. In situ hybridization revealed that the expression of SgPGs and SgPME1 was restricted to mature pollen grains after microspore mitosis. These results suggest that the pollen-specific or anther-specific expression of genes for PGs, PME and GN occurs in a dioecious plant, willow, just as it does in monoecious plants, and that the expression of these genes is related to the developmental stage of pollen grains during male gametogenesis.