CHARACTERIZATION OF GENE EXPRESSION IN ROOTS OF CYPRIPEDIUM PARVIFLORUM VAR. PUBESCENS INCUBATED WITH A MYCORRHIZAL FUNGUS

Temperate, terrestrial orchids have large potential as a novel horticultural crop offering both the exoticism of the orchid flower with superior hardiness. Terrestrial orchids remain a peripheral commodity due, in large part, to the difficulty in propagation and production. The difficulty arises because of a dependence of the orchid on a mycorrhizal fungus for germination and growth. A differential display technique was used to identify genes that show regulation in the early stages of the formation of mycorrhiza in orchids. Cypripedium parviflorum var. pubescens was grown in the presence or absence of Thanatephorus pennatus. RNA was extracted from roots of both treatments and subjected to RTAFLP-DD PCR. Of 5000 bands, 2 were selected as being differentially expressed. One fragment was identified as trehalose-6-phosphate synthase phosphatase (Tps) and the other as nucleotide binding protein (NuBP). Cloning of the full-length genes was accomplished through RACE PCR. Expression was analyzed using RT-PCR. Tps is a multi-copy gene and is down-regulated by mycorrhizal fungi and trehalose, but not affected by a pathogenic fungus. NuBP is up-regulated by mycorrhizal fungi and trehalose but not affected by a pathogenic fungus. The role of these genes in the interaction is discussed.

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