About the Authors
Department of Plant and Microbial Biology, University of California Berkeley, Berkeley, California, United States of America
The authors have declared that no competing interests exist.
The author(s) have made the following declarations about their contributions: Conceived and designed the experiments: MRW JS MF. Performed the experiments: MRW JS BP EL MF. Analyzed the data: MRW JS BP EL DRL SS MF. Contributed reagents/materials/analysis tools: MF. Wrote the paper: MRW JS DRL MF.