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-glucana se (GN) that are expressed specifically in male flowers of the dioecious wi llow (Salix gilgiana Seemen), The structural characteristics of the deduced proteins, designated SgPGs, SgPME1 and SgGN1, respectively, suggest that t hese 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 th eir genes are members of a single family. Although the expression of the Sg PGs, SgPME1 and SgGN1 was specific to male catkins (inflorescences), these genes were found in the genomes of both male and female plants. The express ion of the transcripts of SgPGs, SgPME1 and SgGN1 was regulated development ally in male reproductive organs. Maximal expression of SgPGs and SgPME1 wa s detected when male flowers were fully open and mature, while maximal expr ession of SgGN1 occurred at an earlier time. In situ hybridization revealed that the expression of SgPGs and SgPME1 was restricted to mature pollen gr ains after microspore mitosis. These results suggest that the pollen-specif ic or anther-specific expression of genes for PGs, PME and GN occurs in a d ioecious plant, willow, just as it does in monoecious plants, and that the expression of these genes is related to the developmental stage of pollen g rains during male gametogenesis.