Plant defence against aphids: the PAD4 signalling nexus

Arabidopsis PHYTOALEXIN DEFICIENT4 (PAD4) is an important modulator in mediating defences against green peach aphid. This review summarizes how PAD4 acts as a signalling hub to provide resistance to phloem-feeding aphids. In Arabidopsis thaliana, PHYTOALEXIN DEFICIENT 4 (PAD4) functions as a key player in modulating defence against the phloem sap-feeding aphid Myzus persicae (Sülzer), more commonly known as the green peach aphid (GPA), an important pest of a wide variety of plants. PAD4 controls antibiosis and antixenosis against the GPA. In addition, PAD4 deters aphid feeding from sieve elements on Arabidopsis. In the past few years, substantial progress has been made in dissecting the role of PAD4 and its interaction with other signalling components in limiting aphid infestation. Several key genes/mechanisms involved in providing aphid resistance/susceptibility in Arabidopsis regulate the aphid infestation-stimulated expression of PAD4. Together, PAD4 and its interacting signalling partners provide a critical barrier to curtail GPA colonization of Arabidopsis.