| Summary: | <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>) and <i>Xanthomonas oryzae</i> pv. <i>oryzicola</i> (<i>Xoc</i>) lead to the devastating rice bacterial diseases and have a very close genetic relationship. There are tissue-specificity differences between <i>Xoo</i> and <i>Xoc</i>, i.e., <i>Xoo</i> only proliferating in xylem vessels and <i>Xoc</i> spreading in intercellular space of mesophyll cell. But there is little known about the determinants of tissue-specificity between <i>Xoo</i> and <i>Xoc</i>. Here we show that <i>Xoc</i> can spread in the intercellular spaces of mesophyll cells to form streak lesions. But <i>Xoo</i> is restricted to growth in the intercellular spaces of mesophyll cells on the inoculation sites. In vivo, <i>Xoc</i> largely breaks the surface and inner structures of cell wall in mesophyll cells in comparison with <i>Xoo</i>. In vitro, <i>Xoc</i> strongly damages the cellulose filter paper in comparison with <i>Xoo</i>. These results suggest that the stronger cell wall-degradation ability of <i>Xoc</i> than that of <i>Xoo</i> may be directly determining the tissue-specificity.
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