Overexpression of the MYB-related transcription factor GCC7 in Arabidopsis thaliana leads to increased levels of P and changed P-dependent gene regulation.

A proper concentration and turnover of inorganic phosphate (Pi) is essential to maintain cellular processes. Consequently, plants have mechanisms to control Pi homeostasis and to alleviate Pi limitation. The MYB-related transcription factor, PHR1, is important for gene induction during Pi starvation. PHR1 belongs to a family, characterised by the presence of a GARP- and a coiled coil domain. We propose that this family, with 15 members in Arabidopsis thaliana (L.) Heynh., be termed the GCC-family. In this study, transgenic plants overexpressing one member, GCC7, and a T-DNA knockout mutant, gcc7, are characterised. We find overexpressor plants to accumulate more Pi in shoots, irrespective of the Pi supply. Therefore, GCC7 was characterised in relation to Pi starvation. We conclude that GCC7 is not strictly required for a P-starvation response since the gcc7 mutant responds to Pi limitation. However, overexpression of GCC7 strongly interferes with the P-starvation response, abolishing induction of several P-responsive genes including AT4, IPS1 and several P-transporter genes, whereas GCC7 does not directly interfere with the PHR1 (GCC1) dependent regulation of miR399d. Thus GCC7 influences P-accumulation and P-dependent gene regulation, but GCC7 has a function entirely different from PHR1.