The network of regulatory interactions of MADS-box proteins during floral organ development in Arabidopsis thaliana
Final Report Abstract
Flowers of eudicots like Antirrhinum and Arabidopsis are composed of four concentric whorls, where four different kinds of organs develop: sepal and petals in the two outermost whorls and the reproductive organs, stamens and carpels, in the centre of the flower. Organ development is determined by homeotic genes that interact according to the ABC model. Most of the homeotic genes belong to the family of MADS-box transcription factors. The class B genes APETALA3 and PISTILLATA B from Arabidopsis govern the development petals and stamens, where each organ is composed of different tissues. To unravel how their different contributions to flower organogenesis are realized, protein-protein interactions that involve class B factors were studied using a three-hybrid screening yeast that allowed to isolate new interactors of AP3 and PI. Besides contributing to floral organ identity, MADS-box genes also govern differentiation processes of tissues within the reproductive organs. The MADS- box gene AGL18 was analyzed, which is expressed during pollen development. It is currently common sense to use T-DNA and RNA interference plants to study plant gene functions. Strikingly, knock-out agl18 T-DNA mutants revealed no detectable reproductive phenotypes, whereas the agl18 RNAi plants did exhibit a pollen lethality phenotype and thus indicated that AGL18 seems indeed to affect pollen development. To investigate these contradicting results more thoroughly, a series of transgenic lines using different vectors, promoters and reporter genes was constructed. Analysis of transgenic plants proved that the abnormal pollen development observed in RNAi AGL18 plants is not caused by loss of AGL18 function but rather represents a common feature occurring in transgenic RNAi populations. We could show that pollen lethality is a by-product affecting about 10% of transgenic plants regardless of the construct type used, and the phenomenon is enhanced to more than 20% if RNAi technology is applied to analyze pollen development. Given our observations, it is highly recommendable to combine RNAi data with independent T-DNA mutant analysis and complementation studies to avoid drawing wrong conclusions about gene functions during anther development if only RNAi plants are being analyzed.
Publications
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(2007) Pollen lethality: a phenomenon in Arabidopsis RNA interference plants. Plant Physiology 145, 330-333
Xing, S. and Zachgo, S.
