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.
CJH, JLS, and JBH conceived and designed the experiments. All authors performed the experiments and analyzed the data. CJH, JLS, SMG, and JBH contributed reagents/materials/analysis tools. CJH and JBH wrote the paper.