Abstract Presented at Plant Biology 2019

Sophie Clowez1, Rajnish Khanna1, Tong-Seung Tseng1, Roberto Bogomoln2, and Winslow R. Briggs1.

1Department of Plant Biology, Carnegie Institution for Science, Stanford, CA

2Department of Chemistry, University of California, Santa Cruz, CA

Light-activation of a LOV-histidine kinase in cells of Rhizobium leguminosarum increases the number of nodules and the number of intranodular bacteroids on pea (Pisum sativumL.) roots grown in hydroponics systems (Bonomi et al., Proc. Natl. Acad. Sci. 109: 12135, 2012). We have investigated whether a similar response might be demonstrated under normal greenhouse conditions with pea plants grown in soil to determine whether the finding might ultimately prove beneficial in agriculture. We have also extended the experiments to measure the effects both of light treatment of the bacteria and timing of inoculation on final bean yield. Pre-irradiation of cells of Rhizobium leguminosarum with blue light induces an increase in the number of functional nodules (those containing leghemoglobin) and ultimately seed yield both when the inoculation takes place with the onset of imbibition and four days after the onset when primary roots have emerged. However, inoculation four days after the onset of imbibition and in the presence of primary roots greatly increases both the number of functional nodules and seed yield compared to inoculation at the start of imbibition with or without light treatment of the bacteria. We have measured several growth and developmental parameters, including numbers of flowers per plant per week, pod weight and numbers of peas per pod. Our findings show photoactivated bacterium suppresses floral abortion, and significantly increases pea yield. We are currently carrying out field tests to determine whether light treatment and the timing of inoculation might lead to increased yield in an agricultural context.

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