THE ROLE OF A TPR DOMAIN PROTEIN IN DROUGHT STRESS AND ABSCISIC ACID SIGNAL TANSDUCTION

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0201967
• Grant No.: 2005-35100-15275
• Proposal No.: 2004-02111
• Project Start Date: Nov 15, 2004
• Project End Date: Nov 14, 2006
• Grant Year: 2005
• Program Code: [22.1]- (N/A)

Recipient Organization
DONALD DANFORTH PLANT SCIENCE CENTER
975 NORTH WARSON ROAD
ST. LOUIS,MO 63132

Performing Department
(N/A)

Non Technical Summary
Drought is the most common adverse environmental condition that seriously affects crop productivity worldwide. Plants have certain adaptive mechanisms that could mitigate the damaging effects of drought stress. Discovery of these mechanisms and identification of genes responsible for drought adaptation will be essential for breeding or bioengineering drought tolerant crop plants. We have identified traits in roots that are linked to plant adaptation to drought. Mutants either highly responsive or no longer responsive to drought stress were isolated. Using this approach, we have identified an important regulatory gene that modulates plant drought responses. In this project, the function of this gene in drought tolerance will be studied.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
203	2420	1000	15%
203	2420	1020	15%
203	2420	1030	15%
203	2420	1040	55%

Knowledge Area
203 - Plant Biological Efficiency and Abiotic Stresses Affecting Plants;

Subject Of Investigation
2420 - Noncrop plant research;

Field Of Science
1040 - Molecular biology; 1030 - Cellular biology; 1000 - Biochemistry and biophysics; 1020 - Physiology;

Keywords

drought stress

drought tolerance

abscisic acid

salt tolerance

root development

signal transduction

plant adaptation

stress tolerance

guard cells

plant physiology

protein metabolism

metabolic pathways

cell biology

molecular biology

gene loci

arabidopsis

metabolic regulation

plant genetics

plant development

gene environment interaction

Goals / Objectives
The Arabidopsis GAN locus is a determinant of drought and salt tolerance. The locus also regulates root development in response to drought stress. The GAN gene encodes a TPR (tetratricopepitide repeat) domain-containing protein that is unique to the plant kingdom. This study has two objectives: 1) to determine the in vivo functions of this novel signaling component in stress and abscisic acid signal transduction and in the regulation of developmental adaptation to drought stress and, 2) to define the cellular and molecular targets of the GAN signaling pathway. The relation of GAN to other signaling components will also be investigated.

Project Methods
To determine the function of the GAN gene, we will thoroughly analyze the phenotypes of the knockout mutants and will characterize the GAN gene and its encoded protein using standard procedures. To identify the molecular targets of GAN, we will conduct a genome-wide expression profiling with the loss-of-function gan mutant and will define the GAN-mediated pathways. Further genetic studies will be conducted to establish the relationship between GAN and other components in the ABA and stress signaling pathway or in other related pathways.

Progress 11/15/04 to 11/14/06

Outputs
The genetic basis of crop drought resistance is largely unknown. In this study we developed a genetic system that allows us to analyze drought resistance in the model plant Arabidopsis. The dig (for drought inhibition of lateral root growth) mutants were isolated and characterized. It was found that these mutants not only have altered responses to drought stress in the roots but also exhibit changed drought resistance in the entire plants, indicating that root adaptation to drought stress is intimately linked to whole plant drought resistance. To discover drought resistance mechanisms, we isolated the DIG1 (previously named GAN) gene and further characterized the dig1/gan mutant. About 120 genes were found to have more than 3-fold changes in their expression levels in the mutant. The majority of these genes are implicated in disease resistance as well as abiotic stress responses. Study of several transcription factors that potentially regulate the expression of these genes suggested that they played redundant roles in plant development and stress responses. Since the DIG1 protein is localized in the plastids, these genes appear to be regulated by the plastid-nucleus retrograde signaling pathways. The DIG1 protein may regulate these pathways by modulating redox signaling in the plastids.

Impacts
It has been extremely difficult to reveal the genetic basis of drought resistance. The establishment of a genetic system to analyze drought resistance is the first step toward understanding plant drought tolerance mechanisms. Discovery of genes that control root adaptation to drought and whole plant drought resistance will have implications for breeding drought resistant crop plants.

Publications

• Xiong, L., Wang, R.G., Mao, G., and Koczan, J.M. (2006). Identification of drought tolerance determinants by genetic analysis of root response to drought stress and abscisic Acid. Plant Physiology 142: 1065-1074.
• Xiong L and Ishitani, M. 2006. Stress signal transduction: components, pathways and network integration. In: Abiotic Stress Tolerance in Plants. Ed. Rai, A.K. and Takabe, T. Springer Publishers, Berlin, Germany, 3-29
• Xiong, L. 2007. Abscisic acid in plant response and adaptation to drought and salt stress. In: Advances in molecular-breeding toward drought and salt tolerant crops. Ed. Jenks, MA et al. Springer Publishers (in press).
• Chen H, Hong SW, Xiong L. 2006. Integration of light and abscisic acid signaling during seed germination and early seedling establishment (submitted).

Progress 11/15/04 to 11/15/05

Outputs
The Arabidopsis GAN locus regulates root response to drought stress as well as drought tolerance of the entire plants. The GAN gene was expressed in guard cells and in vascular tissues of roots, stems, and leaves. Microarray and RNA blotting analyses revealed that a specific set of genes were regulated by the GAN locus. The GAN protein also interacts with a small number of proteins with unknown functions. We have showed that one of the GAN-interacting proteins, GIP2 (renamed as PDX1), functions in pyridoxine (vitamin B6) biosynthesis. Like GAN, GIP2 is also required for root development and stress tolerance. Our data suggest that the GAN protein may act as a scaffold in mediating the assembly of novel stress signal transduction complexes.

Impacts
Plant drought tolerance is a very complex trait. A significant number of uncharacterized genes may be involved in drought tolerance. It is thus critical to identify regulatory or key components that orchestrate other components in fine-tuning drought response and drought tolerance. The discovery of the scaffold protein GAN will help us to identify the signaling complexes essential for drought adaptation. Importantly, the GAN protein is highly conserved among crop plants and thus further study of the functionality of the GAN locus will help us to reveal the molecular basis of drought tolerance in all crop plants.

Publications

• Chen H and Xiong L. 2005. Pyridoxine is required for postembryonic root development and tolerance to osmotic and oxidative stresses. The Plant Journal 44: 396-408
• Xiong L and Ishitani, M. 2005. Stress signal transduction: components, pathways and network integration. In: Rai, A.K. and Takabe, T. (Ed). Abiotic Stress Tolerance in Plants. Springer Publishers, Berlin, Germany (in press)