Real Time Live Imaging of Phytopathogenic Bacteria <i>Xanthomonas campestris</i> pv. <i>campestris</i> MAFF106712 in ‘Plant Sweet Home’

<div><p>Xanthomonas is one of the most widespread phytobacteria, causing diseases on a variety of agricultural plants. To develop novel control techniques, knowledge of bacterial behavior inside plant cells is essential. <i>Xanthomonas campestris</i> pv. <i>campestris</i>, a vascular pathogen, is the causal agent of black rot on leaves of Brassicaceae, including <i>Arabidopsis thaliana</i>. Among the <i>X. campestris</i> pv. <i>campestris</i> stocks in the MAFF collection, we selected <i>Xcc</i>MAFF106712 as a model compatible pathogen for the <i>A. thaliana</i> reference ecotype Columbia (Col-0). Using modified green fluorescent protein (AcGFP) as a reporter, we observed real time <i>Xcc</i>MAFF106712 colonization <i>in planta</i> with confocal microscopy. AcGFP-expressing bacteria colonized the inside of epidermal cells and the apoplast, as well as the xylem vessels of the vasculature. In the case of the type III mutant, bacteria colonization was never detected in the xylem vessel or apoplast, though they freely enter the xylem vessel through the wound. After 9 days post inoculation with <i>Xcc</i>MAFF106712, the xylem vessel became filled with bacterial aggregates. This suggests that <i>Xcc</i> colonization can be divided into main four steps, (1) movement in the xylem vessel, (2) movement to the next cell, (3) adhesion to the host plant cells, and (4) formation of bacterial aggregates. The type III mutant abolished at least steps (1) and (2). Better understanding of <i>Xcc</i> colonization is essential for development of novel control techniques for black rot.</p>