The wheat calcium-dependent protein kinase TaCPK7-D positively regulates host resistance to sharp eyespot disease

Sharp eyespot, caused mainly by the necrotrophic fungus Rhizoctonia cerealis, limits wheat production worldwide. Here, TaCPK7-D, encoding a subgroup III member of the calcium-dependent protein kinase (CPK) family, was identified from the sharp eyespot-resistant wheat line CI12633 through comparative transcriptomic analysis. Subsequently, the defence role of TaCPK7-D against R. cerealis infection was studied by the generation and characterization of TaCPK7-D-silenced and TaCPK7-D-overexpressing wheat plants. Rhizoctonia cerealis inoculation induced a higher transcriptional level of TaCPK7-D in the resistant wheat line CI12633 than in the susceptible cultivar Wenmai 6. The expression of TaCPK7-D was significantly induced after exogenous application of 1-aminocyclopropane-1-carboxylic acid (an ethylene biosynthesis precursor). The green fluorescent protein signal distribution assays indicated that TaCPK7-D localizes to the plasma membrane in both onion epidermal cells and wheat protoplasts. Following R. cerealis inoculation, TaCPK7-D-silenced wheat CI12633 plants displayed more severe sharp eyespot symptoms than control CI12633 plants. Four defence-associated genes (β-1,3-glucanase, chitinase 1, defensin and TaPIE1) and an ethylene biosynthesis key gene, ACO2, were significantly suppressed in the TaCPK7-D-silenced wheat plants compared with control plants. Conversely, TaCPK7-D-overexpressing wheat lines showed increased resistance to sharp eyespot compared with untransformed recipient wheat Yangmai 16. Furthermore, the transcriptional levels of these four defence-related genes and ACO2 gene were significantly elevated in TaCPK7-D-overexpressing plants compared with untransformed recipient wheat plants. These results suggest that TaCPK7-D positively regulates the wheat resistance response to R. cerealis infection through the modulation of the expression of these defence-associated genes, and that TaCPK7-D is a candidate to improve sharp eyespot resistance in wheat.