Evolutionary conservation of mycorrhiza-specific phosphate transporter gene regulation by CTTC MOTIF-BINDING TRANSCRIPTION FACTOR1 (CBX1)
L. KLINNAWEE (1), L. Xue (1), M. Bucher (1) (1) Botanical Institute, Cologne Biocenter, University of Cologne, Germany

Mutualism between plants and mycorrhizal fungi is a successful adaptive strategy for host plants to confront phosphate (Pi) deficiency. Mycorrhizal fungi deliver soluble inorganic Pi from remote soil regions to plant roots in exchange with carbohydrates. Mycorrhizal Pi uptake is under the control of mycorrhiza-specific Pi transporter genes, markedly up-regulated by fungal colonization of root cortical cells. Although fundamental cis-regulatory elements including P1BS and CTTC motifs in the respective promoters have been described, the transcription factors activating the symbiotic Pi transporter genes are still unknown. Therefore the objective of this study is to verify the transcription factor (TF) interacting with the CTTC motif in promoters of mycorrhiza-specific Pi transporter genes. In our previous study (Xue et al., 2015), an APETALA2 (AP2) gene in Lotus japonicus roots was significantly up-regulated by mycorrhiza formation under low Pi conditions. In our current work, the AP2 protein was in vitro classified by EMSA as a candidate TF targeting the CTTC motif in a 1.4-kb promoter fragment of the mycorrhiza-specific Pi transporter4 (LjPT4) gene through the use of fluorescence-labeled oligonucleotide probes containing either wildtype or mutated CTTC motifs. The AP2 protein, named CTTC MOTIF-BINDING TRANSCRIPTION FACTOR1 (CBX1), bound specifically to the CTTC cis-regulatory element. Subsequently, nine conserved nucleotides within the motif were shown to constitute the core motif required for DNA binding. Furthermore, functional dissection of CBX1 is currently performed to denominate the binding and activation domains of CBX1. 

Abstract Number: P2-32
Session Type: Poster