EgPHL7, EgPHR1 and EgPHR2 bind to the P1BS and a unique motif, AGATACT for transcriptional regulation of phosphate-starvation inducible genes in oil palm

Oil palm (Elaeis guineensis Jacq.) is an economically important perennial crop in Malaysia that requires a substantial amount of phosphate fertilizer on a regular basis to maintain optimum oil output. Phospate STARVATION RESPONSE 1 (PHR1) and its homologues, PHR1-like 1 (PHL1) and PHR1-like 2 (PHL2), regulate systemic responses in Arabidopsis under Pi deprivation condition, but their function in oil palm remains largely unknown. In this study, a protein designated as EgPHL7 which contains the MYB and coiled-coil (CC) domains, was identified in oil palm. The GFP protein that served as control was detected throughout the entire transformed onion cell, where else the EgPHL7-GFP fusion protein accumulated predominantly in the onion nucleus, confirming nuclear-localization of its encoded product. Our results demonstrated that EgPHL7 and its homologues, EgPHR1 and EgPHR2 can directly bind to P1BS in vitro and in vivo. Notably, a novel cis-acting element, AGATACT motif was identified in the promoter of EgSPX1. This novel motif combined with P1BS to form a P1BS::P1BS-like structure which showed the highest DNA-binding ability with the oil palm MYB-CC transcription factors. Further in silico promoter analysis revealed the present of this novel motif with variant bases in the promoter of several phosphate-starvation induced genes in oil palm. Together, the findings suggest that these MYB-CC TFs may form an integrative regulatory network to manipulate Pi-starvation molecular responses in oil palm. These findings provide new valuable knowledge of the common DNA interaction property between PHR1 family of transcription factors that govern the transcriptional responses under Pi-deficiency stress.

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