Using hydathode-focused inoculation, the study mapped a major QTL on Arabidopsis chromosome 5 and identified the CNL-type immune receptor SUT1 as a novel resistance gene that restricts early colonization of Xanthomonas campestris pv. campestris in hydathodes. Functional analyses showed SUT1 acts independently of the known RKS1/ZAR1 complex and provides tissue‑specific resistance, being effective primarily in hydathodes but not in xylem.