Discovering signaling events in the actinorhizal symbiosis

Although the symbiosis between Frankia and actinorhizal host plants has been widely studied, very little is known about the initial molecular interactions. To address this issue, Casuarina cunninghamiana root exudates were collected and tested on Frankia Ccl3. Frankia growth yield was enhanced by root exudates but Frankia could not utilize them as a sole carbon and energy source. Exposure to root exudates caused Frankia hyphal curling and surface property changes in fatty acids and carbohydrates. Pre-exposure to root exudates also decreased the time required for nodule initiation. The results show that root exudates and Frankia physiological changes for symbiosis are involved in the actinrohizal symbiosis. Frankia auxin production in planta was also researched as a possible signaling molecule. Bioinformatics of auxin synthesis genes and expression analysis of putative Frankia genes revealed Frankia can likely produce auxins in mature nodules, suggesting auxins may be a signaling molecule in the actinorhizal symbiosis