Role ofLONELY GUYgenes in indeterminate nodulation onMedicago truncatula

Abstract

SummaryLONELY GUY (LOG) genes encode cytokinin riboside 5′-monophosphate phosphoribohydrolases and are directly involved in the activation of cytokinins.To assess whether LOG proteins affect the influence of cytokinin on nodulation, we studied two LOG genes of Medicago truncatula.Expression analysis showed that MtLOG1 and MtLOG2 were upregulated during nodulation in a CRE1-dependent manner. Expression was mainly localized in the dividing cells of the nodule primordium. In addition, RNA interference revealed that MtLOG1 is involved in nodule development and that the gene plays a negative role in lateral root development. Ectopic expression of MtLOG1 resulted in a change in cytokinin homeostasis, triggered cytokinininducible genes and produced roots with enlarged vascular tissues and shortened primary roots. In addition, those 35S:LOG1 roots also displayed fewer nodules than the wild-type. This inhibition in nodule formation was local, independent of the SUPER NUMERIC NODULES gene, but coincided with an upregulation of the MtCLE13 gene, encoding a CLAV-ATA3/EMBRYO SURROUNDING REGION peptide.In conclusion, we demonstrate that in M. truncatula LOG proteins might be implicated in nodule primordium development and lateral root formation.

Root developmental programs shape theMedicago truncatulanodule meristem

“…The lower level of auxin signaling in the NCM is, however, sufficient to induce the expression of several auxinresponsive genes (Limpens et al, 2013;Breakspear et al, 2015;Roux et al, 2014). The expression of cytokinin signaling and synthesis genes, such as MtCre1, MtARR4 (Gonzalez-Rizzo et al, 2006;Plet et al, 2011) and MtLOG1 (Mortier et al, 2014), in the NM is in line with our observations on the cytokinin response in the NM. To what extent differences in hormone regimes are instructive in shaping the NVM and the NCM remains to be elucidated.…”

“…In addition, several genes in the cytokinin signaling cascade are reported to be activated in the NM (Frugier et al, 2008;Plet et al, 2011;Mortier et al, 2014). To determine the cytokinin response distribution in the NM we studied the expression of TCS::GUS, a synthetic cytokinin-responsive promoter (Müller and Sheen, 2008), in transgenic Medicago roots and nodules.…”

Flavonoids and Auxin Transport Inhibitors Rescue Symbiotic Nodulation in the Medicago truncatula Cytokinin Perception Mutant cre1

“…Nod factors produced by rhizobia are in most cases necessary and in some legumes sufficient to induce nodules (Truchet et al, 1991). The signaling cascade mediating Nod factor action leads to the activation of cytokinin signaling in the cortex of the root Oldroyd et al, 2011), which is accompanied by activation of the gene encoding the cytokinin biosynthesis enzyme LOG1, a cytokinin riboside 5-monophosphate phosphoribohydrolase (Mortier et al, 2014), and an increase in cytokinin concentration at the nodule initiation site in M. truncatula (van Zeijl et al, 2015). Several studies have implicated cytokinin as a central regulator in nodule development .…”

A Laser Dissection-RNAseq Analysis Highlights the Activation of Cytokinin Pathways by Nod Factors in the Medicago truncatula Root Epidermis

“…An autoactive form of CCamK/DMI3 (snf1 mutant) requires LHK1 to produce spontaneous nodules, while snf2 does not require CCamK/DMI3 to induce spontaneous nodules, indicating that CK/LHK1 acts downstream from CCamK (Tirichine et al, 2007). The CK biosynthesis genes ISOPENTENYL TRANSFERASE3 (IPT3) in L. japonicus and LONELY GUY1 (LOG1) and LOG2 in M. truncatula are up-regulated during nodulation via CRE1/LHK1, while decreasing MtLOG1 or LjIPT3 expression by RNA interference leads to decreased nodulation (Chen et al, 2014;Mortier et al, 2014). The CK-CRE1/LHK1 pathway controls polar auxin transport (Plet et al, 2011;Suzaki et al, 2012) and the Rhizobium spp.…”