The Complex Roles of Plant Hormones During Clubroot Disease Development in the Brassicaceae

Clubroot, caused by the obligate parasite Plasmodiophora brassicae, is a serious soilborne disease that threatens many commercially valuable crops in the Brassicaceae family, including the oilseed crop canola (Brassica napus) and various vegetables. Evidence from studies analyzing hormonal profiles, transcriptomes, proteomes, mutants defective in hormone functions, and treatments of infected plants with growth regulators suggest that nearly all plant hormones are involved in or affected by the disease. However, the specific roles of individual hormones in clubroot development or resistance remain unclear. This knowledge gap is compounded by the complex regulation of hormone functions and inconsistencies across studies, likely due to variations caused by host-pathogen combinations and other factors such as environmental influences. Additionally, biotic and abiotic stress responses caused by the disease and, in some instances, pathogen proteins manipulating host hormonal metabolism add additional layers of complexity. Despite these challenges, emerging trends suggest regulatory roles for plant hormones in both disease development and host defense. In this review, we explore these patterns, aiming to elucidate the contributions of different hormones to clubroot development and associated stress responses.