Expression analysis of the gastrodianin gene ga4B in an achlorophyllous plant Gastrodia elata Bl.

Gastrodia elata Bl. is an achlorophyllous orchid plant feeding on the fungus Armillaria mellea. The plant lives underground during its life cycle except for florescence. Gastrodianins, members of the superfamily of monocot mannose-binding protein (MBP), have been identified from Gastrodia elata, yet their physiological functions in the plant are rarely understood. Aspects of expression of gastrodianins in growth and development of the plant will be helpful to dissect their functional roles. Two types of cDNA clones with complete cDNA sequences matching the known gastrodianins were obtained from G. elata Bl.f.glauca S.chow (Orchidaceae) and designated gastrodianin-4A (ga4A) and gastrodianin-4B (ga4B), respectively. But only one isoform was found to be expressed in all different parts of a single plant. Based on the RNA gel blot analysis, gastrodianins were much more abundantly expressed in the fully opened flowers than the underground corms where an enhanced expression was found in the out layers of secondary corms. By RNA in situ hybridization gastrodianin transcripts were distinctly detected in the cortical cells and vascular cells of corms. Strong transcript accumulations were observed in two to eight layers of cortical cells in secondary corms. From its peripheral tissue expression pattern and level in corms and flowers, the gastrodianin may account for a possible defense against phytopathogens or insects.