ABSTRACT Xanthomonas campestris pv. campestris (Xcc) is a Gram‐negative bacterium that causes black rot, leading to significant economic losses in global cabbage production. To date, the dynamic colonization and transmission mechanisms of Xcc in cabbage via three major infection routes (seeds, leaves, and roots) remain largely elusive. In this study, we developed a bioluminescent Xcc strain using a modified Tn1409 transposon carrying the luxCDABE operon, enabling real‐time visualization of bacterial colonization in cabbage. Among eight bioluminescent mutant strains generated, BJSJQ20200612‐pXX3‐4 exhibited the highest luminescence intensity without compromising bacterial growth or pathogenicity. The bioluminescent strain with stable and constitutive expression, BJSJQ20200612‐pXX3‐4, was used to observe the real‐time Xcc colonization in cabbage using leaf‐clipping, root‐dipping, and seed‐soaking inoculation methods. Xcc translocated from the cut blade edge along the veins to the petiole and eventually to the stem by the leaf‐clipping inoculation. Xcc effectively invades plants from the roots, spreading through the vascular bundles to the stems and leaves using the root‐dipping inoculation. Xcc moves from seed coat throughout hypocotyl to leaves via the vascular system with the seed‐soaking inoculation, with no bioluminescence detected in the roots. Xcc can establish initial infection more rapidly through seeds compared to other methods. Scanning electron microscopy was used to confirm that Xcc colonizes cabbage vascular tissues, with formation of bacterial aggregates in xylem vessels of hypocotyls. Taken together, our findings establish a robust non‐invasive real‐time monitoring system for Xcc infection in cabbage, and provide novel insights into the Xcc‐cabbage interaction. This well‐characterized bioluminescent strain is a powerful tool for deciphering Xcc pathogenesis, screening black rot‐resistant germplasm, and developing targeted disease management strategies.
Zhong et al. (Sun,) studied this question.