6 research outputs found
PHO2-Dependent Degradation of PHO1 Modulates Phosphate Homeostasis in Arabidopsis
The Arabidopsis thaliana pho2 mutant, which is defective in a ubiquitin-conjugating E2 enzyme, displays inorganic phosphate
(Pi) toxicity as a result of enhanced uptake and root-to-shoot translocation of Pi. To elucidate downstream components of the
PHO2-dependent regulatory pathway, we identified two pho2 suppressors as carrying missense mutations in PHO1, which
has been implicated in Pi loading to the xylem. In support of the genetic interaction between PHO1 and PHO2, we found that
the protein level of PHO1 is increased in pho2, whereas such accumulation is ameliorated in both pho2 suppressors. Results
from cycloheximide and endosomal Cys protease inhibitor E-64d treatments further suggest that PHO1 degradation is PHO2
dependent and involves multivesicular body–mediated vacuolar proteolysis. Using the transient expression system of
tobacco (Nicotiana tabacum) leaves, we demonstrated that PHO1 and PHO2 are partially colocalized and physically interact
in the endomembranes, where the ubiquitin conjugase activity of PHO2 is required for PHO1 degradation. In addition, reduced
PHO1 expression caused by PHO1 mutations impede Pi uptake, indicating a functional association between xylem loading
and acquisition of Pi. Together, our findings uncover a pivotal molecular mechanism by which PHO2 modulates the
degradation of PHO1 in the endomembranes to maintain Pi homeostasis in plants