Abstract
The symbiosis receptor kinase SymRK plays an essential role in symbiotic signal transduction and nodule organogenesis. Several proteins bind to SymRK, but how the symbiosis signals are transduced from SymRK to downstream components remains elusive. We previously demonstrated that both SymRK interacting protein 1 (SIP1, an ARID-type DNA-binding protein) and SymRK interacting E3 ligase [SIE3, a RING (Really Interesting New Gene)-containing E3 ligase] interact with SymRK to regulate downstream cellular responses in Lotus japonicus during the legume-rhizobia symbiosis. Here, we show that SIE3 interacts with SIP1 in both yeast cells and Nicotiana benthamiana. SIE3 associated with itself and formed a homodimer. The cysteine 266 residue was found to be essential for SIE3 dimerization and for promoting nodulation in transgenic hairy roots of L. japonicus. Our findings provide a foundation for further investigating the regulatory mechanisms of the SymRK-mediated signaling pathway, as well as the biological function of E3 ligase dimerization in nodule organogenesis.
Highlights
The establishment of the rhizobia-legume symbiosis is a tightly regulated process that integrates bacterial infection steps with specialized organ development
We previously demonstrated that Symbiosis receptor-like kinase (SymRK) interacts with both SymRK interacting protein 1 (SIP1), an ARID-type transcription factor and SymRK-interacting E3 ligase (SIE3), a RING-type E3 ubiquitin ligase in L. japonicus (Zhu et al, 2008; Yuan et al, 2012)
These results indicate that SIE3 associates with SIP1 in yeast cells
Summary
The establishment of the rhizobia-legume symbiosis is a tightly regulated process that integrates bacterial infection steps with specialized organ development. NF action is accompanied by a series of signal transduction processes inside root cells. Intense research has focused on elucidating NF signaling, which plays an essential role in nodule organogenesis (Dénarié et al, 1996; Oldroyd and Downie, 2008; Masson-Boivin et al, 2009). Genetic dissection of nodulation in legumes such as Medicago truncatula and Lotus japonicus has led to the discovery of NF receptors and several key players in the NF signaling pathway (Oldroyd and Downie, 2004, 2006). Symbiosis receptor-like kinase (SymRK) is required for symbiotic signal transduction upon stimulation of root cells by microbial signaling molecules (Endre et al, 2002; Stracke et al, 2002). The exact biochemical functions and regulatory mechanisms of SymRK remain unknown
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