Infection of the Rice Root Xylem by Xanthomonas oryzae pv. oryzae and Inability to Migrate from Roots to Shoots...

Xanthomonas oryzae pv. oryzae (Xoo), the causal agent of bacterial blight in rice, has primarily been studied in the context of foliar infections. However, infected stubble and irrigation water may serve as reservoirs and be responsible for root infections at the seedling stage in the field, especially during transplanting. Here, we established a coleoptile crown root infection protocol to investigate whether TAL effectors can induce SWEET sucrose uniporter susceptibility genes in the root and whether the disease can propagate from roots to seedling shoots. Using translational SWEET11a-GUS reporter rice lines under control of the native SWEET11a promoter, we observed progressive infection in the root xylem after clip infection of roots, as indicated by accumulation of the SWEET11a-GUS fusion protein in infected coleoptile crown roots. However, we did not detect progression of GUS accumulation beyond the coleoptile node, nor did we detect bacterial blight symptoms on the young leaves. Notably, the xylem, at least during the early stages of infection, remained functional, as shown by Rhodamine B tracers, consistent with transfer of xylem constituents via living cells at the coleoptile nodes that did not allow bacteria to pass. The root clip infection protocol is approximately 4× faster compared with standard leaf-clipping assays (root assay: 11 days from sowing; clip infection: 39 days), enabling rapid assessment of the TAL effector activity and plant defense responses with translational SWEET-GUS reporter rice lines. Our findings expand our understanding of Xoo infection routes and provide a valuable tool for resistance testing and pathogen surveillance. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.