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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION AND ENHANCEMENT OF PLANT RESISTANCE TO WATER-DEFICIT AND THERMAL STRESSES

Location: Plant Stress and Germplasm Development Research

2012 Annual Report


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 completed protein profiling of peanut pod development and drought stress responses. We are continuing to sequence differentially expressed proteins identified during the profiling to reveal genes contributing to drought tolerance. 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. The molecular basis of this 'off target' effect appears to be associated with alterations to the plant's microRNA and trans-acting small interfering RNA populations that result from transgene silencing. 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 F7 stage and are being evaluated for their drought responses. 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.


4.Accomplishments
1. Cotton diversity revealed in Fusarium wilt-resistant lines. Continuous improvement of yield, fiber quality, and disease resistance of cotton breeding lines is important to maintain the competitiveness of U.S. cotton. A scientist recently joining the Plant Stress and Germplam Development Unit assayed more than 2000 in-house breeding lines for resistance to races 1 and 4 of the causal organism of Fusarium wilt in greenhouse and field studies. Observed disease responses revealed interactions between individual cotton entries and race of Fusarium. Analyses to investigate the inheritance of Fusarium wilt resistance and to identify associated genes were initiated. Ten Pima breeding lines with resistance to Fusarium wilt were evaluated for yield potential and fiber quality at two field locations representing different soil types. Upon release, these breeding lines will expand the genetic base available to cotton breeders for development of Fusarium resistant cultivars.

2. Yield enhancement technology for dryland cotton. Plant growth and development can be inhibited by early season drought. Scientists within the Plant Stress and Germplam Development Unit in Lubbock, Texas, have discovered a novel process for enhancing the growth and development of cotton under drought conditions. Application of relatively low concentrations of a naturally occurring plant hormone called a cytokinin to cotton seed or to young cotton plants increased cotton yields under rainfed conditions. These findings provide a means of increasing dryland yields without any adverse effects on irrigated cotton production.

3. Gene expression patterns can be tracked for peanuts. Peanut, being an under-represented crop in terms of genome sequencing and physical mapping, needs a comprehensive tool for dissecting complex mechanisms of development and tolerance to insects, diseases, and environmental stresses. Scientists within the Plant Stress and Germplam Development Unit in Lubbock, Texas, have developed a tool to analyze changes in the expression of 49,205 peanut genes, and tested the utility of this tool on a variety of peanut tissues. This is the first large-scale, publicly available tool for determining which peanut genes are active out of all of the genes that exist within the peanut plant. The results generated by this tool will provide starting points for in-depth studies on candidate genes that can be utilized in reverse genetics to assign gene functions and identify specific molecular mechanisms of peanut response of environmental signals, developmental stages, and yield quality characteristics.

4. Gene silencing by interfering RNAs identified. A gene inserted into tobacco controlling anthocyanin (purple) pigment production is subject to spontaneous post-transcriptional gene silencing in a heavily pigmented plant line. Scientists within the Plant Stress and Germplam Development Unit in Lubbock, Texas, have shown that under certain genetic conditions, silencing of the transgene appears to impact normal plant growth and development, producing stunted plants with severely malformed leaves. The molecular basis of this 'off target' effect appears to be associated with alterations to the plant's microRNA and trans-acting small interfering RNA populations that result from transgene silencing. Understanding the mechanisms plants use to silence genes is essential for future improvements in abiotic stress tolerance.


Review Publications
Burke, J.J. 2011. 6-Benzyladenine enhancement of cotton. Journal of Cotton Science. 15(3):206-214.

Gitz, D.C., Xin, Z., Baker, J.T., Lascano, R.J., Burke, J.J. 2012. Effect of solar loading on greenhouse containers used in transpiration efficiency screening. Agronomy Journal. 104(2):388-392.

Kottapalli, P., Upadhyaya, H., Kottapalli, K.R., Payton, P.R., Dwivedi, S., Burow, M., Puppala, N. 2011. Assessing genetic diversity in Valencia peanut germplasm using SSR markers. Crop Science. 51:1089-1100.

Pasapula, V., Shen, G., Kuppu, S., Paez-Valencia, J., Mendoza, M., Hou, P., Chen, J., Qui, X., Zhu, L., Zhang, X., Auld, D., Blumwald, E., Zhang, H., Gaxiola, R., Payton, P.R. 2010. Expression of an arabidopsis vacuolar H+-pyrophosphatase gene (AVP1) in cotton improves drought- and salt tolerance and increases fibre yield in the field conditions. Plant Biotechnology Journal. 8(5):1-12.

Mahan, J.R., Young, A., Payton, P.R. 2012. Deficit irrigation in a production setting; Canopy temperature as an adjunct to ET estimates. Irrigation Science. 30(2):127.

Ulloa, M., Wang, C., Hutmacher, R.B., Wright, S.D., Davis, R.M., Saski, C.A., Roberts, P.A. 2011. Mapping Fusarium wilt race 1 resistance genes in cotton by inheritance, QTL and sequencing composition. Molecular Genetics and Genomics. 286:21-36.

Last Modified: 9/21/2014
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