Restricted transmission of Xanthomonas oryzae pv. oryzae from rice roots to shoots detected by a rapid root infection system

Abstract

Xanthomonas oryzae pv. oryzae ( Xoo ), the causal agent of bacterial blight in rice, is primarily studied in the context of foliar infections. However, infected stubble and irrigation water may serve as reservoirs and be responsible for seedling stage root infections in the field, especially during transplanting. Here, we established a coleoptile crown root-based infection protocol to investigate whether gene-for-gene interactions between Xoo TAL effectors and SWEET sucrose uniporter susceptibility genes occur in the root xylem, and whether the disease can propagate from roots to seedling shoots. Using translational SWEET11a-GUS reporter lines under control of the native SWEET11a promoter, we observed progressive infection as indicated by accumulation of 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 blight symptoms on the young leaves. Notably, the xylem, at least during early stages of infection remained functional as shown by Rhodamine B tracer, consistent with transfer of xylem constituents via living cells at the coleoptile node that did not allow bacteria to pass. Furthermore, the root infection protocol is a ∼4x faster compared to standard leaf-clipping assays (roots assay: 11 days from sowing, compared to 39 days for clip infection), enabling more rapid assessment of TAL effector repertoire and plant defense responses with translational SWEET-GUS reporter lines. Our findings expand our understanding of Xoo infection routes and provide a valuable tool for resistance testing and pathogen surveillance.

Plant phenotyping relevance

イネ病害の進展・抵抗性を迅速に評価する根部感染プロトコルを確立し、従来法との速度差とレポーターによる感染進展を示しているため、病害フェノタイピング手法が中心である。

Code and data availability

The preprint explicitly states that raw data underlying the root infection, GUS, and Rhodamine B measurements are publicly deposited at a DOI (10.60534/7s2cg-r2j06), which is an allowed URL. This is a paper-specific, publicly accessible raw data repository. No author analysis code with a public URL is stated (only use-