Seven in Absentia Proteins Affect Plant Growth and Nodulation inMedicago truncatula   

Abstract

Protein ubiquitination is a posttranslational regulatory process essential for plant growth and interaction with the environment. E3 ligases, to which the seven in absentia (SINA) proteins belong, determine the specificity by selecting the target proteins for ubiquitination. SINA proteins are found in animals as well as in plants, and a small gene family with highly related members has been identified in the genome of rice (Oryza sativa), Arabidopsis (Arabidopsis thaliana), Medicago truncatula, and poplar (Populus trichocarpa). To acquire insight into the function of SINA proteins in nodulation, a dominant negative form of the Arabidopsis SINAT5 was ectopically expressed in the model legume M. truncatula. After rhizobial inoculation of the 35S:SINAT5DN transgenic plants, fewer nodules were formed than in control plants, and most nodules remained small and white, a sign of impaired symbiosis. Defects in rhizobial infection and symbiosome formation were observed by extensive microscopic analysis. Besides the nodulation phenotype, transgenic plants were affected in shoot growth, leaf size, and lateral root number. This work illustrates a function for SINA E3 ligases in a broad spectrum of plant developmental processes, including nodulation.

Comparison of Developmental and Stress-Induced Nodule Senescence in Medicago truncatula

“…Similar features have been described in aberrant nodules of Fix 2 mutants or transgenic plants or induced by lipopolysaccharidedefective bacteria (Perotto et al, 1994;Tsyganov et al, 1998;Campbell et al, 2002;Suganuma et al, 2003;Wan et al, 2007;Den Herder et al, 2008).…”

TheMedicago truncatulaE3 Ubiquitin Ligase PUB1 Interacts with the LYK3 Symbiotic Receptor and Negatively Regulates Infection and Nodulation

“…However, this conclusion needs to await the completion of the M. truncatula genome sequencing project and the functional characterization of other legume proteins in the PUB1 subclade. Several E3 ubiquitin ligases have been shown to be regulated and/or play a role in nodulation (Nishimura et al, 2002;Karlowski and Hirsch, 2003;Shimomura et al, 2006;Den Herder et al, 2008;Kiss et al, 2009;Yano et al, 2009). These E3 ubiquitin ligases belong to other subfamilies than PUB1 and have rather different protein structures.…”

Lotus japonicus E3 Ligase SEVEN IN ABSENTIA4 Destabilizes the Symbiosis Receptor-Like Kinase SYMRK and Negatively Regulates Rhizobial Infection

“…SINA dimers were shown to be the active form in plants (Xie et al, 2002), but in mammalian cells, SINA also participates in an Skp Cullin F-Box-like complex (Santelli et al, 2005). Plant SINA families comprise highly conserved proteins with six members in Arabidopsis thaliana and rice, and 10 in poplar (Populus trichocarpa; Den Herder et al, 2008;Wang et al, 2008). In Arabidopsis, SINAT5 regulates lateral root numbers via specific targeting of the NAC1 transcription factor (Xie et al, 2000(Xie et al, , 2002, and SINAT2 interacts with the RAP2.2 transcription factor (Welsch et al, 2007).…”

“…In M. truncatula, introduction of the Arabidopsis dominant-negative SINAT5DN form resulted in a symbiotic infection phenotype (Den Herder et al, 2008).…”