Promoters of OrthologousGlycine maxandLotus japonicusNodulation Autoregulation Genes Interchangeably Drive Phloem-Specific Expression in Transgenic Plants

Abstract

The nodule autoregulation receptor kinase (GmNARK) of soybean (Glycine max) is essential for the systemic autoregulation of nodulation. Based on quantitative reverse-transcriptase polymerase chain reaction, GmNARK is ex-pressed to varying levels throughout the plant; the transcript was detected at high levels in mature leaves and roots but to a lesser extent in young leaves, shoot tips, and nodules. The transcript level was not significantly affected by Bradyrhizobium japonicum during the first week following inoculation. In addition, the activities of the promoters of GmNARK and Lotus japonicus HARI, driving a beta-glucuronidase (GUSPlus) reporter gene, were examined in stably transformed L. japonicus and transgenic hairy roots of soybean. Histochemical GUS activity in L. japonicus plants carrying either a 1.7-kb GmNARKpr::GUS or 2.0-kb LjHAR1pr::GUS construct was clearly localized to living cells within vascular bundles, especially phloem cells in leaves, stems, roots, and nodules. Phloem-specific expression also was detected in soybean hairy roots carrying these constructs. Our study suggests that regulatory elements required for the transcription of these orthologous genes are conserved. Moreover, rapid amplification of 5' cDNA ends (5' rapid amplification of cDNA ends) revealed two major transcripts of GmNARK potentially originating from two TATA boxes. Further analysis of the GmNARK promoter has confirmed that these two TATA boxes are functional. Deletion analysis also located a region controlling phloem-specific expression to a DNA sequence between 908 bp and 1.7 kb upstream of the translation start site of GmNARK.

The receptor-like kinase KLAVIER mediates systemic regulation of nodulation and non-symbiotic shoot development in Lotus japonicus

“…The functional requirement of KLV and HAR1 in the shoot suggests that the shoot is a crucial compartment that monitors and regulates root nodule development. The HAR1 expression pattern is consistent with a recent report that the HAR1 promoter is active in the vascular bundle, especially in the phloem (Nontachaiyapoom et al, 2007). It has been proposed that the putative root-derived signal molecule(s) are transported through the vascular tissues to the shoot .…”

The ROOT DETERMINED NODULATION1 Gene Regulates Nodule Number in Roots of Medicago truncatula and Defines a Highly Conserved, Uncharacterized Plant Gene Family

“…Such long-distance communication presumably involves the movement of signaling molecules through the vascular cylinder. The promoter of the SUNN gene is active in the vasculature throughout the plant (A. Karve and J. Frugoli, unpublished data), as has also been found for its orthologs LjHAR1 and GmNARK, reported as active predominantly in the phloem (Nontachaiyapoom et al, 2007). Reporter gene analysis in roots shows that like the SUNN promoter, the RDN1 promoter appears to be active in cells of the vasculature although its activity appears to be more widespread than the SUNN promoter (Fig.…”

TheM. truncatula SUNNgene is expressed in vascular tissue, similarly toRDN1, consistent with the role of these nodulation regulation genes in long distance signaling

“…These results were consistent with those of Nontachaiyapoom et al who examined the orthologous soybean NARK and Lotus HAR1 promoters in a L. japonicus background. 8 They reported sequence conservation between the promoters of the Lotus, Medicago and Glycine orthologs including a sequence element driving vascular specific expression and our results confirm this experimentally in the Medicago background.…”