Systemic control mechanism of root nodule formation via phytochrome signaling

Abstract

We found two mutants of Lotus japonicus, which were having elongated shoot and had elongated hypocotyls when germinate under red light. Subsequent sequencing analysis revealed to have mutations in the PHYB gene of both lines. Both mutants formed lesser number of nodules compared to the wild type.
Grafting experiments using phyB mutant showed that shoot genotype is responsible for the negative regulation of root nodulation. One possible reason for low nodule number inphyB mutants is due to limiting photosynthates. How about another reason? L. japonicus which was grown under continuous white light for 14 days was moved to high R:FR or low R:FR condition and then nodulation test were carried out. Surprisingly, the number of root nodules of low R:FR plants was dramatically reduced compared with that of high R:FR plants. These results indicate that root nodule formation is one of the R:FR ratio perception reaction.