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Transformation and Regeneration of Taro with Two Plant Disease Resistance Genes: A Rice Chitinase Gene and a Wheat Oxalate Oxidase Gene

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Title:Transformation and Regeneration of Taro with Two Plant Disease Resistance Genes: A Rice Chitinase Gene and a Wheat Oxalate Oxidase Gene
Authors:He, Xiaoling
Date Issued:2006
Abstract:Taro {Colocasia esculenta) is one of the most important crops in the Pacific Islands. However, taro yields have been declining in Hawaii over the past 30 years due to diseases caused by oomycete and fungal pathogens. Chitin, an important structural component of the cell wall of most fungi, is hydrolyzed by the action of the enzyme chitinase. Plants transformed with a chitinase gene have shown increased resistance to several fungal pathogens. Oxalate oxidase, which converts oxalic acid and O2 to CO2 and H2O2 , has been shown to be involved in plant resistance to pathogens. Transformation of plants with an oxalate oxidase gene has increased their resistance to fungal pathogens.
An efficient regeneration and transformation system of the taro cultivar Bun Long has been developed. Regenerable calli were induced on MS medium with 2 mg L-1 BA and 1 mg L-1 NAA (M5 medium). Multiple shoots from these calli were induced on MS medium supplemented with 4 mg L-1 BA (M15 medium). The rice chitinase gene (RICCHIll) was introduced into taro calli using particle bombardment. Analyses using polymerase chain reaction (PCR) and Southern blot confirmed the presence of the rice chitinase gene in one transgenic line.
Agrobacterium tumefaciens-mediated transformation using two plant disease resistance genes: a rice chitinase gene (RICCHIl 1) and a wheat oxalate oxidase gene (gf2.8) were developed. Two hundred calli were infected with the supervirulent A. tumefaciens strain EHA105 harboring the plant transformation plasmid pBI121:RICCHI11. Six lines were shown to contain the rice chitinase gene using the PCR and Southern blot analyses. Transformation was also conducted using EHA105:pB1121:gf2.8 that contains the wheat oxalate oxidase gene gf2.8. Two independent lines were shown to be positive for the specific gf2.8 gene fragment using PCR, Southern blot and RT-PCR analyses, indicating the presence and transcription of gf2.8 gene in the transformed lines. In a preliminary bioassay, six transgenic taro lines with the rice chitinase gene exhibited tolerance to the fungal pathogen Sclerotium rolfsii. One transgenic taro line with the wheat oxalate oxidase gene showed tolerance to both the fungal pathogen Sclerotium rolfsii and oomycete pathogen Phytophthora colocasiae.
To our knowledge, this is the first report of taro transformed with disease resistance genes. In addition, this is the first report of genetically engineered taro that exhibited disease tolerance in preliminary bioassays.
Appears in Collections: Ph.D. - Horticulture

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