The M. truncatula SUNN gene is expressed in vascular tissue, similarly to RDN1, consistent with the role of these nodulation regulation genes in long distance signaling
Elise Schnabel, Abhijit Karve, Tessema Kassaw, Arijit Mukherjee, Xin Zhou, Tim Hall and Julia Frugoli
1 January 2012, Plant Signaling and Behavior 7(1): 4-6; doi: 10.4161/psb.7.1.18491
Encoding a conserved protein of unknown function, the Medicago truncatula RDN1 gene is involved in autoregulation of nodulation through signaling in the root. In contrast, the SUNN kinase in M. truncatula has been shown by grafting of mutant scions to control nodule number in the root by communication of a signal from the shoot to the root. GUS staining patterns resulting from expression of the SUNN promoter fused to uidA showed expression of SUNN in most parts of plant including the root, but confined to the vascular tissue, a pattern that overlaps with that published for RDN1. Real Time qRT-PCR analysis showed levels of both SUNN RNA and RDN1 RNA did not change significantly during early nodulation signaling (072 h after inoculation). The similarity in expression in cell types strongly suggests vascular signaling for nodule number regulation, while the lack of changes over early nodule development suggest post transcriptional mechanisms such as protein association or phosphorylation transmit the signal.
Expression of a SUNNpro:mGFP-GUS fusion in wild-type plants. A Nikon E600 microscope with a Retiga EXi-FAST monochrome CCD 12-bit camera was used for visualization and imaging of some stained samples and a Zeiss Lumar.V12 stereoscope equipped with AxioCAM MRC and AxioVision software (Zeiss) for others. Leaf, stem and root transverse sections were made by hand using a razor blade. The sections were routinely ~0.2mm in thickness. (A) Staining in the veins in leaflets; (B) cross section of petioles; (C) cross section of leaflet with arrows indicating staining in vasculature; (D) cross section of stem; (E) close up of stem showing staining in phloem; (F) cross section of root; (G) mature nodules; (H) cross section of root and nodule and (I) faint staining in the vasculature leading to the meristem from the same plant used for (E), but no meristematic staining.
The M. truncatula SUNN gene is expressed in vascular tissue, similarly to RDN1, consistent with the role of these nodulation regulation genes in long distance signaling Elise Schnabel, Abhijit Karve, Tessema Kassaw, Arijit Mukherjee, Xin Zhou, Tim Hall, Julia Frugoli Plant Signal Behav. 2012 January 1; 7(1): 46. doi: 10.4161/psb.7.1.18491