Find in Library

The typical symptom of Paulownia witches’ broom (PaWB), caused by phytoplasma infection, is excessive branching, which is mainly triggered by auxin metabolism disorder. <i>Aux/IAA</i> is the early auxin-responsive gene that participates in regulating plant morphogenesis such as apical dominance, stem elongation, lateral branch development, and lateral root formation. However, no studies have investigated the response of the <i>Aux/IAA</i> gene family to phytoplasma infection in <i>Paulownia fortunei</i>. In this study, a total of 62 <i>Aux/IAA</i> genes were found in the genome. Phylogenetic analysis showed that <i>PfAux/IAA</i> genes could be divided into eight subgroups, which were formed by tandem duplication and fragment replication. Most of them had a simple gene structure, and several members lacked one or two conserved domains. By combining the expression of <i>PfAux/IAA</i> genes under phytoplasma stress and SA-treated phytoplasma-infected seedlings, we found that <i>PfAux/IAA13/33/45</i> may play a vital role in the occurrence of PaWB. Functional analysis based on homologous relationships showed a strong correlation between <i>PfAux/IAA45</i> and branching. Protein–protein interaction prediction showed that PfARF might be the binding partner of PfAux/IAA, and the yeast two-hybrid assay and bimolecular fluorescent complementary assay confirmed the interaction of PfAux/IAA45 and PfARF13. This study provides a theoretical basis for further understanding the function of the <i>PfAux/IAA</i> gene family and exploring the regulatory mechanism of branching symptoms caused by PaWB.