title: A Developmental and Molecular View of Formation of Auxin-Induced Nodule-Like Structures in Land Plants.
abstract: Several studies have shown that plant hormones play important roles during legume-rhizobia symbiosis. For instance, auxins induce the formation of nodule-like structures (NLSs) on legume roots in the absence of rhizobia. Furthermore, these NLS can be colonized by nitrogen-fixing bacteria, which favor nitrogen fixation compared to regular roots and subsequently increase plant yield. Interestingly, auxin also induces similar NLS in cereal roots. While several genetic studies have identified plant genes controlling NLS formation in legumes, no studies have investigated the genes involved in NLS formation in cereals. In this study, first we established an efficient experimental system to induce NLS in rice roots, using auxin,2,4-D, consistently at a high frequency (>90%). We were able to induce NLS at a high frequency inMedicago truncatulaunder similar conditions. NLS were characterized by a broad base, a diffuse meristem, and increased cell differentiation in the vasculature. Interestingly, NLS formation appeared very similar in both rice andMedicago, suggesting a similar developmental program. We show that NLS formation in both rice andMedicagooccurs downstream of the common symbiotic pathway. Furthermore, NLS formation occurs downstream of cytokinin-induced step(s). We performed a comprehensive RNA sequencing experiment to identify genes differentially expressed during NLS formation in rice and identified several promising genes for control of NLS based on their biological and molecular functions. We validated the expression patterns of several genes using reverse transcription polymerase chain reaction and show varied expression patterns of these genes during different stages of NLS formation. Finally, we show that NLS induced on rice roots under these conditions can be colonized by nitrogen-fixing bacteria,Azorhizobium caulinodans.
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Hiltenbrand
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Jacklyn
authors.initials: J
authors.lastname: Thomas
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Hannah
authors.initials: H
authors.lastname: McCarthy
authors.affiliation: Bioinformatics and Biostatistics Core, Van Andel Research Institute, Grand Rapids MI, USA.
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Dykema
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Ashley
authors.initials: A
authors.lastname: Spurr
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Hamilton
authors.initials: H
authors.lastname: Newhart
authors.affiliation: Bioinformatics and Biostatistics Core, Van Andel Research Institute, Grand Rapids MI, USA.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Winn
authors.affiliation: Department of Biology, University of Central Arkansas, Conway AR, USA.
authors.forename: Arijit
authors.initials: A
authors.lastname: Mukherjee
keywords: Azorhizobium caulinodans; Medicago truncatula; RNA sequencing; auxin; common symbiotic pathway; nodule-like structures; rice