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

Abstract

<i>Plasmodiophora brassicae</i> is a soil borne pathogen and the causal agent of clubroot, a devastating disease of <i>Brassica</i> crops. 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 underlying <i>P. brassicae</i> infection and sugar transport is unclear. Here, we analyzed sugar contents in leaves and roots before and after <i>P. brassicae</i> infection using a pair of Chinese cabbage near-isogenic lines (NILs), carrying either a clubroot resistant (CR) or susceptible (CS) allele at the <i>CRb</i> locus. <i>P. brassicae</i> infection caused significant increase of glucose and fructose contents in the root of CS-NIL compared to CR-NIL, suggesting that sugar translocation and <i>P. brassicae</i> growth are closely related. Among 32 <i>B. rapa SWEET</i> homologs, several <i>BrSWEETs</i> belonging to Clade I and III were significantly up-regulated, especially in CS-NIL upon <i>P. brassicae</i> infection. Moreover, <i>Arabidopsis sweet11</i> mutant exhibited slower gall formation compared to the wild-type plants. Our studies suggest that <i>P. brassicae</i> infection probably triggers active sugar translocation between the sugar producing tissues and the clubbed tissues, and the <i>SWEET</i> family genes are involved in this process.