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

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