The transport of monolignols from the cytosol to the cell wall is essential for lignin synthesis. The ATP-binding cassette (ABC) transporters may be involved in the transport of lignin precursors. ABC transporter genes subjected to expression analysis were chosen based on two criteria for screening candidate transporter genes related to lignification. The expression levels of 15 target genes in five plant organs were analyzed by real-time PCR. Five transporter genes (ABCG29, ABCG30, ABCG33, ABCG34, and ABCG37), which were simultaneously expressed with the reference genes, were selected as candidates. The candidate gene expression levels in root tissues of T-DNA insertion mutants were determined by semi-quantitative reverse transcription PCR. ABCG30 was more highly expressed in the abcg34 mutant than in the wild-type plants, while the expression of ABCG34 was twofold higher in the abcg30 mutant plants than in the wild-type plants. Thus, the expression of ABCG30 and ABCG34 may affect each other. There was no significant change in lignin content and composition in the single-gene knockout mutants of the candidate transporter genes, which suggested that each candidate gene did not solely contribute to lignin synthesis.
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