Nitrate-inducible MdBT2 acts as a restriction factor to limit apple
necrotic mosaic virus genome replication in Malus domestica
Abstract
Apple necrotic mosiac virus (ApNMV) is a newly identified causal agent
that is highly associated with the occurrence of apple mosaic disease in
China. However, resistance gene against this virus has not been
identified yet. We reported here that nitrate treatment destablized
viral protein 1a via the ubiquitin-proteasome pathways to restrain ApNMV
genomic RNA accumulation. A nitrate-responsive BTB/TAZ domain-containing
protein MdBT2 was identified in a yeast-two-hybrid screening of apple
cDNA library using viral protein 1a as bait, and 1a was confirmed to
interact with MdBT2 both in vivo and in vitro. MdBT2 was further
verified to promote the ubiquitination and degradation of viral protein
1a through the proteasome pathways in a MdCUL3A-scaffold protein in E3
ligase complex-independent manner. Viral genomic RNA accumulation was
decreased in MdBT2 overexpression transgenic apple leaves but enhanced
in MdBT2 antisense leaves compared to that in wild type. Moreover, MdBT2
was found to interfere with the interactions between viral replication
proteins 1a and 2apol by competing with the latter. Taken together, our
work demonstrated that nitrate-inducible MdBT2 functioned as a limiting
factor in ApNMV viral RNA accumulation by promoting the ubiquitination
and degradation of viral protein 1a and interfering with the
interactions between viral replication proteins.