Abstract
A C subunit of the heterotrimeric nuclear factor Y (NF-YC1) was shown to play a key role in nodule organogenesis and bacterial infection during the nitrogen fixing symbiosis established between common bean (Phaseolus vulgaris) and Rhizobium etli. To identify other proteins involved in this process, we used the yeast (Saccharomyces cerevisiae) two-hybrid system to screen for NF-YC1-interacting proteins. One of the positive clones encodes a member of the Phytochrome A Signal Transduction1 subfamily of GRAS (for Gibberellic Acid-Insensitive (GAI), Repressor of GAI, and Scarecrow) transcription factors. The protein, named Scarecrow-like13 Involved in Nodulation (SIN1), localizes both to the nucleus and the cytoplasm, but in transgenic Nicotiana benthamiana cells, bimolecular fluorescence complementation suggested that the interaction with NF-YC1 takes place predominantly in the nucleus. SIN1 is expressed in aerial and root tissues, with higher levels in roots and nodules. Posttranscriptional gene silencing of SIN1 using RNA interference (RNAi) showed that the product of this gene is involved in lateral root elongation. However, root cell organization, density of lateral roots, and the length of root hairs were not affected by SIN1 RNAi. In addition, the expression of the RNAi of SIN1 led to a marked reduction in the number and size of nodules formed upon inoculation with R. etli and affected the progression of infection threads toward the nodule primordia. Expression of NF-YA1 and the G2/M transition cell cycle genes Cyclin B and Cell Division Cycle2 was reduced in SIN1 RNAi roots. These data suggest that SIN1 plays a role in lateral root elongation and the establishment of root symbiosis in common bean.
Highlights
A C subunit of the heterotrimeric nuclear factor Y (NF-YC1) was shown to play a key role in nodule organogenesis and bacterial infection during the nitrogen fixing symbiosis established between common bean (Phaseolus vulgaris) and Rhizobium etli
Because we have previously shown that NF-YC1 mRNAs increase in roots at early time points after R. etli inoculation (Meschini et al, 2008; Zanetti et al, 2010), we examined the accumulation of SCL13 Involved in Nodulation1 (SIN1) transcripts at 24 h post inoculation and 4 dpi
We identified a member of the plantspecific family of GRAS proteins through its physical interaction with NF-YC1
Summary
A C subunit of the heterotrimeric nuclear factor Y (NF-YC1) was shown to play a key role in nodule organogenesis and bacterial infection during the nitrogen fixing symbiosis established between common bean (Phaseolus vulgaris) and Rhizobium etli. NSP1 and NSP2 are essential for nodulation, mediating different nuclear factor-induced responses, such as root hair deformation, IT formation, cortical cell divisions, and expression of nodulin genes (Catoira et al, 2000; Oldroyd and Long, 2003; Kaló et al, 2005; Smit et al, 2005) Both proteins are involved in mycorrhization (Liu et al, 2011), together with Required for Arbuscular Mycorrhization (RAM1), which plays a specific role in the formation of arbuscular mycorrhiza through its interaction with NSP2 but is dispensable for nodule formation (Gobbato et al, 2012). The heterotrimeric nature of NF-Y complexes, the association with other classes of transcription factors, and the expansion of the gene family of each subunit in plants result in a flexible combinatorial system that provides the versatility required to integrate endogenous and exogenous signals, allowing plants to growth and adapt to changing environmental conditions
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