Genome Wide Identification and Expression Profiling of SWEET Genes Family Reveals Its Role During Plasmodiophora brassicae-Induced Formation of Clubroot in Brassica rapa

Hong Li, Xiaonan Li, Yuanhu Xuan, Jing Jiang, Yangdou Wei, Zhongyun Piao

Plasmodiophora brassicae is a soil borne pathogen and the causal agent of clubroot, a devastating disease ofBrassicacrops. The pathogen lives inside roots, and hijacks nutrients from the host plants. It is suggested that clubroot galls created an additional nutrient sink in infected roots. However, the molecular mechanism underlyingP. brassicaeinfection and sugar transport is unclear. Here, we analyzed sugar contents in leaves and roots before and afterP. brassicaeinfection using a pair of Chinese cabbage near-isogenic lines (NILs), carrying either a clubroot resistant (CR) or susceptible (CS) allele at theCRblocus.P. brassicaeinfection caused significant increase of glucose and fructose contents in the root of CS-NIL compared to CR-NIL, suggesting that sugar translocation andP. brassicaegrowth are closely related. Among 32B. rapa SWEEThomologs, severalBrSWEETsbelonging to Clade I and III were significantly up-regulated, especially in CS-NIL uponP. brassicaeinfection. Moreover,Arabidopsis sweet11mutant exhibited slower gall formation compared to the wild-type plants. Our studies suggest thatP. brassicaeinfection probably triggers active sugar translocation between the sugar producing tissues and the clubbed tissues, and theSWEETfamily genes are involved in this process.