Floral induction in tissue culture: a system for the analysis of LEAFY-dependent gene regulation

• Published in: The Plant journal : for cell and molecular biology Vol. 39; no. 2; pp. 273 - 282
• Main Authors: Wagner, D, Wellmer, F, Dilks, K, William, D, Smith, M.R, Kumar, P.P, Riechmann, J.L, Greenland, A.J, Meyerowitz, E.M
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-07-2004; Blackwell Science
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Biological and medical sciences; Biology and morphogenesis of the reproductive apparatus. Photoperiodism, vernalisation; callus; Culture Techniques - methods; floral induction; floral meristem identity; flower development; flowering; Flowers - growth & development; Fundamental and applied biological sciences. Psychology; gene expression analysis; gene expression regulation; Gene Expression Regulation, Plant; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; in vitro regeneration; LEAFY; MADS Domain Proteins; microarray technology; micropropagation; Oligonucleotide Array Sequence Analysis; Plant physiology and development; plant proteins; Plant Proteins - genetics; Plant Proteins - metabolism; Plant Shoots - growth & development; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; tissue culture; transcription factors; Transcription Factors - genetics; Transcription Factors - metabolism; Vegetative and sexual reproduction, floral biology, fructification; gene expression analysis; callus; Genomics; floral meristem identity; floral induction; Gene expression; Arabidopsis thaliana; Induced flowering; Gene; LEAFY; Cruciferae; Dicotyledones; Angiospermae; flower development; Spermatophyta; Transcription factor
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2004.02127.x

We have developed a versatile floral induction system that is based on ectopic overexpression of the transcription factor LEAFY (LFY) in callus. During shoot regeneration, flowers or floral organs are formed directly from root explants without prior formation of rosette leaves. Morphological and reporter gene analyses show that leaf-like structures are converted to floral organs in response to LFY activity. Thus, increased levels of LFY activity are sufficient to bypass normal vegetative development and to direct formation of flowers in tissue culture. We found that about half of the cultured cells respond to inducible LFY activity with a rapid upregulation of the known direct target gene of LFY, APETALA1 (AP1). This dramatic increase in the number of LFY-responsive cells compared to whole plants suggested that the tissue culture system could greatly facilitate the analysis of LFY-dependent gene regulation by genomic approaches. To test this, we monitored the gene expression changes that occur in tissue culture after activation of LFY using a flower-specific cDNA microarray. Induction of known LFY target genes was readily detected in these experiments. In addition, several other genes were identified that had not been implicated in signaling downstream of LFY before. Thus, the floral induction system is suitable for the detection of low abundance transcripts whose expression is controlled in an LFY-dependent manner.