ORIGINAL ARTICLE Yinbo Gan Æ Sophie Filleur Æ Azizur Rahman Susan Gotensparre Æ Brian G. Forde Nutritional regulation of ANR1 and other root-expressed MADS-box genes in Arabidopsis thaliana Received: 15 February 2005 / Accepted: 10 May 2005 / Published online: 15 July 2005 Ó Springer-Verlag 2005 Abstract The ANR1 MADS-box gene in Arabidopsis thaliana (L.) Heynh. has previously been identified as a key regulator of lateral root growth in response to sig- nals from external nitrate (NO 3  ). We have used quan- titative real-time PCR to investigate the responsiveness of ANR1 and 11 other root-expressed MADS-box genes to fluctuations in the supply of N, P and S. ANR1 expression in roots of hydroponically grown Arabidopsis plants was specifically regulated by changes in the N supply, being induced by N deprivation and rapidly re- pressed by N re-supply. This pattern of N responsiveness differs from the NO 3  -inducibility of ANR1 previously observed in Arabidopsis root cultures [H.M. Zhang and B.G. Forde (1998) Science 279:407–409]. Seven of the other MADS-box genes responded to N in a manner similar to ANR1, but less strongly, while four (AGL12, AGL17, AGL18 and AGL79) were unaffected. Six of the N-regulated genes (ANR1, AGL14, AGL16, AGL19, SOC1 and AGL21) belong to just two clades within the type II MADS-box lineage, while the other two (AGL26 and AGL56) belong to the poorly characterized type I lineage. Only SOC1 was additionally found to respond to changes in the P and S supply, suggesting a possible role in a general response to nutrient stress. Studies with an ANR1 transposon-insertion mutant provided no evidence for regulatory interactions between ANR1 and the other root-expressed MADS-box genes. The impli- cations of the current data for our understanding of the role of ANR1 and other MADS box genes in the nutritional regulation of lateral root growth are dis- cussed. Keywords Gene expression Æ Knock-out mutant Æ mRNA Æ Nitrogen Æ Quantitative real-time PCR Æ Roots Abbreviations DIG: Digoxigenin Æ KO: Knock-out Æ NAA: 1-naphthalene acetic acid Æ qRT-PCR: Quantitative real-time PCR Æ SSC: Saline sodium citrate Introduction When plants are exposed to major fluctuations in their nutrient supply, they respond with an extensive re-pro- gramming of metabolism, as well as adaptive modifica- tions at the level of growth and development. Profound changes in gene expression are known to precede and accompany these metabolic and morphological adjust- ments (Wu et al. 2003; Hirai et al. 2004; Scheible et al. 2004; Wang et al. 2004), but the signal transduction pathways and regulatory mechanisms that convert changes in nutrient availability into the appropriate set of molecular and cellular responses are poorly under- stood. The Arabidopsis ANR1 gene has been identified as a component of a signalling pathway that regulates lat- eral root growth in response to changes in the external NO 3 supply (Zhang and Forde 1998). ANR1 encodes a member of the MADS-box family of transcription factors, which has over 100 members in Arabidopsis B. G. Forde (&) Department of Biological Sciences, Lancaster University, Bailrigg Lancaster, LA1 4YQ, UK E-mail: b.g.forde@lancaster.ac.uk Tel.: +15-24-510207 Fax: +15-24-843854 Y. Gan Centre for Novel Agricultural Products, University of York, Heslington, York, Y010 5DD UK S. Filleur Institut des Sciences Ve`ge´tales CNRS, 1 Avenue de la Terrasse, 91198 Gif-sur-Yvette, France A. Rahman Department of Horticulture, Bangladesh Agricultural University, Mymensingh, 2202 Bangladesh S. Gotensparre Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berks, RG20 7NN UK Planta (2005) 222: 730–742 DOI 10.1007/s00425-005-0020-3