Arginase-negative mutants of Arabidopsis exhibit increased NO signaling in root development

FLORES TERESITA; TODD CHRISTOPHER; TOVAR-MENDEZ ALEJANDRO; DHANOA PREETINDER K; CORREA-ARAGUNDE NATALIA; HOYOS MARY ELIZABETH; BROWNFIELD DISA M; MULLEN ROBERT T.; LAMATTINA LORENZO; POLACCO JOE C

PLANT PHYSIOLOGY.

American Society of Plant Biologists

Año: 2008 vol. 147 p. 1936 - 1946

0032-0889

Mutation of either arginase structural gene (ARGAH1 or ARGAH2) resulted in increased formation of lateral and adventitious roots in Arabidopsis seedlings and increased nitric oxide (NO) accumulation and efflux, detected by the fluorogenic traps, DAF FM-DA and DAR-4M,respectively. Upon seedling exposure to synthetic auxin, naphthalene acetic acid, NO accumulation was differentially enhanced in argah1-1 and argah2-1 compared to the progenitor. In all genotypes much DAF FM-DA fluorescence originated from mitochondria. The arginases are both localized to the mitochondrial matrix and are closely related. However, their expression levels and patterns differ: ARGAH1 encoded the minor activity, and ARGAH1-driven GUS was expressed throughout the seedling; the ARGAH2::GUS expression pattern was more localized. Both naphthalene acetic acid and NO donor sodium nitroprusside increased seedling lateral root numbers (total lateral roots per primary root). However, lateral roots in the mutants were increased twice as much as in the wild type- patterns consistent with increased internal NO leading to enhanced auxin signaling in roots. In agreement, argah1-1 and argah2-1 showed increased expression of the auxin-responsive reporter, DR5::GUS, in root tips, emerging lateral roots and hypocotyls. We propose that arginine, or an arginine derivative, is a potential NO source, and that reduced arginase activity in the mutants results in greater conversion of Arg to NO, thus potentiating auxin action in roots. The model is supported by supplemental arginine induction of adventitious roots and of increased NO accumulation in argah1-1 and argah2-1 versus wild type.