Foliar sugar accumulation enhances priming of the salicylic acid-mediated defense response

Pierre Gebauer ¹ Martin Korn ¹ Timo Engelsdorf ^1,2 Uwe Sonnewald ¹ Christian Koch ¹ Lars Voll lars.voll@biologie.uni-marburg.de ^1,3

¹Division of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
²Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway
³Department of Biology, Philipps-University Marburg, Marburg, Germany

We have investigated the role of carbohydrate partitioning and allocation in Arabidopsis source leaves in the compatible interaction with the fungal hemibiotroph Colletotrichum higginsianum, which exhibits an initial biotrophic and an ensuing necrotrophic colonization phase.

Arabidopsis mutants with impaired starch turnover are more susceptible towards C. higginsianum infection and a strong negative correlation between diurnal carbohydrate accumulation and fungal proliferation is evident in the investigated mutants. Our results demonstrate that mutants suffering from nocturnal carbon shortage show a dampened salicylic acid (SA) response that impairs defense especially during the necrotrophic colonization phase.

On the other hand, Arabidopsis double mutants lacking the sucrose transporters SWEET11 and SWEET12 show constantly elevated carbohydrate levels and are more resistant towards C. higginsianum. Analysis of YFP reporter plants as well as single and double mutants suggests that a lack of these transporters does not affect pathogen nutrition during the initial biotrophic phase. Instead, our data identify enhanced priming of the SA pathway in sweet11/sweet12 double mutant as the cause of increased resistance.