ABA plays a central role in mediating the regulatory effects of nitrate on root branching in Arabidopsis.

The formation of lateral roots (LR) is a major post-embryonic developmental event in plants. In Arabidopsis thaliana, LR development is inhibited by high concentrations of NO3(-). Here we present strong evidence that ABA plays an important role in mediating the effects of NO3(-) on LR formation. Firstly, the inhibitory effect of NO3(-) is significantly reduced in three ABA insensitive mutants, abi4-1, abi4-2 and abi5-1, but not in abi1-1, abi2-1 and abi3-1. Secondly, inhibition by NO3(-) is significantly reduced, but not completely abolished, in four ABA synthesis mutants, aba1-1, aba2-3, aba2-4 and aba3-2. These results indicate that there are two regulatory pathways mediating the inhibitory effects of NO3(-) in A. thaliana roots. One pathway is ABA-dependent and involves ABI4 and ABI5, whereas the second pathway is ABA-independent. In addition, ABA also plays a role in mediating the stimulation of LR elongation by local NO3(-) applications.

[1]  P. Benfey,et al.  Down and out in Arabidopsis: the formation of lateral roots , 1997 .

[2]  C. Rock,et al.  The aba mutant of Arabidopsis thaliana is impaired in epoxy-carotenoid biosynthesis. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[3]  C. M. Karssen,et al.  The isolation and characterization of abscisic acid-insensitive mutants of Arabidopsis thaliana , 1984 .

[4]  P W Barlow,et al.  Dual pathways for regulation of root branching by nitrate. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[5]  H. Goodman,et al.  Isolation of the Arabidopsis ABI3 gene by positional cloning. , 1992, The Plant cell.

[6]  W. Frommer,et al.  Identification of mutants in metabolically regulated gene expression. , 1997, The Plant journal : for cell and molecular biology.

[7]  S. Smeekens,et al.  Photosynthesis, sugars and the regulation of gene expression. , 2000, Journal of experimental botany.

[8]  N. Chua,et al.  Sucrose control of phytochrome A signaling in Arabidopsis. , 1997, The Plant cell.

[9]  P. Weisbeek,et al.  The Arabidopsis SUCROSE UNCOUPLED-6 gene is identical to ABSCISIC ACID INSENSITIVE-4: involvement of abscisic acid in sugar responses. , 2000, The Plant journal : for cell and molecular biology.

[10]  S. Gibson,et al.  The Arabidopsis sugar-insensitive mutants sis4 and sis5 are defective in abscisic acid synthesis and response. , 2000, The Plant journal : for cell and molecular biology.

[11]  J. Micol,et al.  Genetic analysis of salt-tolerant mutants in Arabidopsis thaliana. , 2000, Genetics.

[12]  B. Forde,et al.  An Arabidopsis MADS box gene that controls nutrient-induced changes in root architecture. , 1998, Science.

[13]  T. Lynch,et al.  The Arabidopsis Abscisic Acid Response Gene ABI5 Encodes a Basic Leucine Zipper Transcription Factor , 2000, Plant Cell.

[14]  P. Benfey,et al.  Organization and cell differentiation in lateral roots of Arabidopsis thaliana. , 1997, Development.

[15]  P. León,et al.  Analysis of Arabidopsis glucose insensitive mutants, gin5 and gin6, reveals a central role of the plant hormone ABA in the regulation of plant vegetative development by sugar. , 2000, Genes & development.

[16]  S. Jacobsen,et al.  Isolation and characterization of abscisic acid-deficient Arabidopsis mutants at two new loci. , 1996, The Plant journal : for cell and molecular biology.

[17]  H. Goodman,et al.  The Arabidopsis Abscisic Acid Response Locus ABI4 Encodes an APETALA2 Domain Protein , 1998, Plant Cell.

[18]  J. Giraudat,et al.  Arabidopsis ABA response gene ABI1: features of a calcium-modulated protein phosphatase. , 1994, Science.

[19]  S. Merlot,et al.  The Arabidopsis ABSCISIC ACID-INSENSITIVE2 (ABI2) and ABI1 genes encode homologous protein phosphatases 2C involved in abscisic acid signal transduction. , 1997, The Plant cell.

[20]  B. Forde,et al.  Regulation of Arabidopsis root development by nitrate availability. , 2000, Journal of experimental botany.