XPNPEP2 and infection: To determine whether MAMP perception in B. rapa could protect plants from infection, we measured the growth of the bacterial pathogen Xanthomonas campestris campestris (hereafter Xcc), the causal agent of black rot disease in Brassica crops, in leaves pre-treated for 24 h with elf18, chitin or flg22 (Fig. 6a).