Date of Award

January 2016

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Botany and Plant Pathology

First Advisor

Jin-Rong Xu

Committee Member 1

Charles P Woloshuk

Committee Member 2

Stephen B Goodwin

Committee Member 3

Steven R Scofield


The cAMP-dependent protein kinase A (PKA) signal transduction pathway plays an important role in morphogenesis and virulence in plant pathogenic fungi. In the rice blast fungus Magnaporthe oryzae, it regulates surface recognition, appressorium turgor generation, and invasive growth. Two genes in M. oryzae named CPKA and CPK2 encode the catalytic subunits of cAMP-dependent protein kinase A. Previous studies have shown that deletion of CPKA failed to block response to exogenous cAMP, suggesting the involvement of CPK2 in cAMP signaling. To further characterize the function of the catalytic subunits of PKA in infection-related development in M. oryzae, we generated the cpkA cpk2 double mutant. The double mutant had severe growth and conidiation defects. It was non-pathogenic though the intracellular cAMP level and activation of the Pmk1 MAP kinase were increased. Interestingly, the double mutant spontaneously produced fast-growing suppressors after cultivation on oatmeal agar plates over ten days. Twenty fast-growing suppressors were isolated and characterized. Sequencing analysis showed that loss-of-function mutations in MoSFL1 were responsible for the rescue of growth defects of the cpkA cpk2 mutant. MoSfl1 acts as a transcription repressor by interacting with the Cyc8-Tup1 co-repressor. The interaction between MoSfl1 and Cyc8-Tup1 is relieved by phosphorylation of MoSfl1 by PKA, which is important for normal hyphal growth. In the suppressor strains, loss-of-function mutations in MoSfl1 bypassed the requirement of PKA phosphorylation to release its inhibitory binding with the Cyc8-Tup1 co-repressor complex. In this study, we provide new insights into the role of the catalytic subunits of PKA in growth and development and implicate that its negative effect on the transcription repressor MoSfl1 is required for hyphal growth in M. oryzae.