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Nodulin 22, a Novel Small Heat-Shock Protein of the Endoplasmic Reticulum, Is Linked to the Unfolded Protein Response in Common Bean

January 2014 , Volume 27 , Number  1
Pages  18 - 29

Jonathan Rodriguez-López,1 Cynthia Martínez-Centeno,1 Annamalai Padmanaban,2 Gabriel Guillén,1 Juan Elías Olivares,1 Giovanni Stefano,3 Fernando Lledías,1 Fernando Ramos,4 Said A. Ghabrial,2 Federica Brandizzi,3 Mario Rocha-Sosa,1 Claudia Díaz-Camino,1 and Federico Sanchez1

1Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Av. Universidad 2001, Colonia Chamilpa, CP 62210, Cuernavaca, Morelos, México; 2Department of Plant Pathology, 201F Plant Science Building, University of Kentucky, 1405 Veterans Drive, Lexington, KY 40546-0312, U.S.A.; 3Michigan State University-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, U.S.A.; 4Computer Science Department, ITESM Cuernavaca Campus, Morelos, México

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Accepted 5 September 2013.

The importance of plant small heat shock proteins (sHsp) in multiple cellular processes has been evidenced by their unusual abundance and diversity; however, little is known about their biological role. Here, we characterized the in vitro chaperone activity and subcellular localization of nodulin 22 of Phaseolus vulgaris (PvNod22; common bean) and explored its cellular function through a virus-induced gene silencing–based reverse genetics approach. We established that PvNod22 facilitated the refolding of a model substrate in vitro, suggesting that it acts as a molecular chaperone in the cell. Through microscopy analyses of PvNod22, we determined its localization in the endoplasmic reticulum (ER). Furthermore, we found that silencing of PvNod22 resulted in necrotic lesions in the aerial organs of P. vulgaris plants cultivated under optimal conditions and that downregulation of PvNod22 activated the ER-unfolded protein response (UPR) and cell death. We also established that PvNod22 expression in wild-type bean plants was modulated by abiotic stress but not by chemicals that trigger the UPR, indicating PvNod22 is not under UPR control. Our results suggest that the ability of PvNod22 to suppress protein aggregation contributes to the maintenance of ER homeostasis, thus preventing the induction of cell death via UPR in response to oxidative stress during plant-microbe interactions.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2014.