Distinct Temporal Responses to Xanthomonas translucens Strains Shape Bacterial Leaf Streak Development in Triticale

Bacterial leaf streak, brought about by Xanthomonas translucens, poses a significant threat to cereal production. However, the sequential alignment of host transcriptional responses during interactions between resistant and susceptible strains within polyploid crops remains somewhat unclear. To shed light on this issue, researchers employed time-resolved transcriptomics to investigate the reactions of synthetic hexaploid triticale to two X. translucens pv. undulosa strains, each generating distinct disease outcomes.

The resistant interaction with the non-virulent LB10 strain demonstrated a robust initial transcriptional response that subsequently diminished, while the virulent strain P3 elicited responses that gradually grew more intense as water-soaking symptoms emerged.

Upon scrutinizing syntenic A-, B-, and R-subgenome homoeologs, the study uncovered a notable degree of regulatory asymmetry, with R-subgenome homoeologs being disproportionately represented among transcriptionally downregulated genes. Despite possessing identical coding sequences, these homoeologs typically exhibited divergent transcriptional responses during infection. Moreover, a stronger similarity in upstream regulatory regions was linked to more synchronized responsive trajectories.

The researchers further explored the role of pathogen-mediated transcriptional regulation through transcription activator-like (TAL) effectors. Among the eight TAL effector candidates identified in LB10 and P3, TAL5-associated predicted targets demonstrated the most pronounced preferential induction during P3 infection. In P3, the disruption of TAL5 led to a significant reduction in host gene expression, encompassing genes implicated in immune signaling, cell wall-associated defense, and photosynthetic functionality.

This reduction was accompanied by a decrease in maximum photosystem II quantum efficiency at 72 hours post-inoculation.

In conclusion, the findings underscore that bacterial leaf streak outcomes are influenced by temporally distinct host responses and pathogen effector-associated transcriptional reprogramming. This insight offers valuable understanding into the complex and dynamic regulation underlying cereal-Xanthomonas interactions.