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PvRACK1 Loss-of-Function Impairs Cell Expansion and Morphogenesis in Phaseolus vulgaris L. Root Nodules

July 2011 , Volume 24 , Number  7
Pages  819 - 826

Tania Islas-Flores,1 Gabriel Guillén,1 Xóchitl Alvarado-Affantranger,1 Miguel Lara-Flores,2 Federico Sánchez,1 and Marco A. Villanueva3

1Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, and 2Departamento de Genómica Funcional de Eucariotes, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 510-3, Cuernavaca, Morelos 62250, México; 3Instituto de Ciencias del Mar y Limnología, Unidad Académica de Sistemas Arrecifales, UNAM, Prolongación Avenida Niños Héroes S/N, Puerto Morelos, Quintana Roo 77580, México

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Accepted 11 March 2011.

Receptor for activated C kinase (RACK1) is a highly conserved, eukaryotic protein of the WD-40 repeat family. Its peculiar β-propeller structure allows its interaction with multiple proteins in various plant signal-transduction pathways, including those arising from hormone responses, development, and environmental stress. During Phaseolus vulgaris root development, RACK1 (PvRACK1) mRNA expression was induced by auxins, abscissic acid, cytokinin, and gibberellic acid. In addition, during P. vulgaris nodule development, PvRACK1 mRNA was highly accumulated at 12 to 15 days postinoculation, suggesting an important role after nodule meristem initiation and Rhizobium nodule infection. PvRACK1 transcript accumulation was downregulated by a specific RNA interference construct which was expressed in transgenic roots of composite plants of P. vulgaris inoculated with Rhizobium tropici. PvRACK1 downregulated transcript levels were monitored by quantitative reverse-transcription polymerase chain reaction analysis in individual transgenic roots and nodules. We observed a clear phenotype in PvRACK1-knockdown nodules, in which nodule number and nodule cell expansion were impaired, resulting in altered nodule size. Microscopic analysis indicated that, in PvRACK1-knockdown nodules, infected and uninfected cells were considerably smaller (80 and 60%, respectively) than in control nodules. In addition, noninfected cells and symbiosomes in silenced nodules showed significant defects in membrane structure under electron microscopy analysis. These findings indicate that PvRACK1 has a pivotal role in cell expansion and in symbiosome and bacteroid integrity during nodule development.

© 2011 The American Phytopathological Society