Jasmonates, gibberellins, and powdery mildew modify cell cycle progression and evoke differential spatiotemporal responses along the barley leaf.

Barley (Hordeum vulgare) is an important cereal crop, and its development, defence, and stress responses are modulated by different hormones including jasmonates (JAs) and the antagonistic gibberellins (GAs). Barley productivity is severely affected by the foliar biotrophic fungal pathogen Blumeria hordei. In this study, primary leaves were used to examine the molecular processes regulating responses to methyl-jasmonate (MeJA) and GA to B. hordei infection along the leaf axis. Flow cytometry, microscopy, and spatiotemporal expression patterns of genes associated with JA, GA, defence, and the cell cycle provided insights on cell cycle progression and on the gradient of susceptibility to B. hordei observed along the leaf. Notably, the combination of B. hordei with MeJA or GA pre-treatment had a different effect on the expression patterns of the analysed genes compared to individual treatments. MeJA reduced susceptibility to B. hordei in the proximal part of the leaf blade. Overall, distinctive spatiotemporal gene expression patterns correlated with different degrees of cell proliferation, growth capacity, responses to hormones, and B. hordei infection along the leaf. Our results highlight the need to further investigate differential spatial and temporal responses to pathogens at the organ, tissue, and cell levels in order to devise effective disease control strategies in crops.