1a. Objectives (from AD-416)
(1) Identify and functionally characterize genes central to the adaptation of plant to water-deficit and thermal stresses. (2) Discover and/or develop germplasm enhanced for stress resistance traits. (3) Identify and characterize water-deficit and thermal stress-responding promoters for using the controlled expression of stress resistance genes and for testing of a user-friendly plant stress reporter system for crop management.
1b. Approach (from AD-416)
A multidisciplinary research approach will be utilized because of the complexity of the problems to be addressed. Genes will be identified via expression databases and mutational analyses. Physiological and molecular characterizations will be used to identify germplasm with enhanced stress tolerances. Transformational technologies will be used in the development of plant with enhanced stress tolerances and plant with stress responsive reporter genes.
3. Progress Report
We are currently sequencing differentially expressed proteins identified during the profiling to reveal genes contributing to drought tolerance. We completed protein profiling of peanut pod development and drought stress responses. We studied a transgene controlling anthocyanin pigment production that is subject to spontaneous post-transcriptional gene silencing in a heavily pigmented plant line. Under certain genetic conditions silencing of the transgene appears to impact normal plant growth and development, producing stunted plants with severely malformed leaves. Determining the molecular basis of this 'off target' effect will help prevent unwanted plant architectures in plant improvement programs expressing transgenes. To understand molecular mechanisms of heat tolerance in plants, we studied a chloroplast and mitochondria dual targeted protein, identified as essential for plant survival at moderately high temperatures. Our study showed that FtsH11 plays critical roles in both the early stages of chloroplast biogenesis and in maintaining chloroplast structural stability at elevated temperatures. Furthermore, targeted expression of AtFtsH11 in either the chloroplast (cTP-FtsH11) or the mitochondria (mTP-FtsH11) have showed that only chloroplast-targeting of FtsH11 is required for normal chloroplast development and normal photosynthetic functions of plants at moderate high temperatures. We have identified the genes and associated metabolic pathways involved in the water-deficit stress response in cotton leaves and roots. Gene expression profiles were developed for leaf and root tissues subjected to slow-onset water deficit under controlled, glasshouse conditions. Profiling experiments revealed 2,106 stress-responsive transcripts, 879 classified as stress-induced, 1,163 stress-repressed, and 64 showed reciprocal expression patterns in root and leaf. The majority of stress-responsive transcripts had tissue-specific expression patterns, and only 173 genes showed similar patterns of stress-responsive expression in both tissues. We continued the development of plant populations exhibiting differential sensitivity to high temperature exposure. A recombinant inbred population of a cross between the Arabidopsis ecotypes CS1444 and CS1572 has been developed, with 800 individuals at the F7 stage. We are currently phenotyping and genotyping the individual recombinant lines. We are also developing recombinant inbred lines for pollen dehydration avoidance from cotton bi-directional crosses between Phytogen 72 and Stoneville 474. Five hundred recombinant inbred lines are currently in the F6 stage. We evaluated 20 maize inbred lines for drought and/or heat tolerance under greenhouse conditions. Fifteen of the 20 maize inbred lines were evaluated under well-watered and drought-stressed conditions in the field. Lines exhibiting distinctive drought tolerance characteristics are being crossed to produce F1 hybrids that will be evaluated for drought tolerance, yield stability, and maternal effects in field in the next growing season.
1. Assay for heat-tolerant peanut lines. Heat is a major abiotic stress that adversely affects crop production worldwide. Because field screening for heat tolerance can be inconsistent and seasonally limited, ARS scientists in Lubbock, Texas, in cooperation with Texas AgriLife and New Mexico State University scientists, developed a straightforward laboratory protocol using acquired thermotolerance in peanut seedlings as a measure of heat stress tolerance. Evaluation of selected accessions of the US peanut minicore collection along with standard checks showed acquired thermotolerance values were highly correlated with field performance. This method is relatively simple and inexpensive and can be used to screen a large number of genotypes. The technique will result in faster releases of new and improved peanut varieties.
2. Development of cotton lines with improved drought tolerance. Many cotton varieties with excellent fiber quality are very sensitive to the heat and dry conditions associated with drought. ARS scientists in Lubbock, Texas, have developed a family of lines from crosses between a high fiber quality line and a drought-tolerant line. Offspring from these parents contain a mixture of traits from both parents. Selected individuals from these lines that can withstand drought and exhibit excellent fiber quality will be provided to the cotton industry to accelerate the development of new drought-tolerant cotton varieties.
Baek, D., Jiang, J., Chung, J., Chen, J., Xin, Z., Shi, H. 2011. Regulated AtHKT1 gene expression by a distal enhancer element and DNA methylation in the promoter plays an important role in salt tolerance. Plant Cell Physiology. 52(1):149-161.