1a. Objectives (from AD-416):
1. Quantitatively evaluate molecular, biochemical, and structural changes of fiber tissues in cotton plants grown in the field under well-watered, deficit irrigation, and dryland conditions. 2. Evaluate the impacts of different levels of drought stress on fiber quality and lint and seed yields, and analyze the relation of fiber quality traits with those changes detected in objective 1.
1b. Approach (from AD-416):
Transgenic cotton lines harboring CesA1-GUS reporter gene construct will be planted in the research field of USDA-ARS-CSRL at Lubbock, Texas. Two irrigation levels controlled by underground dripping irrigation systems will be applied to study the effect of drought stress on fiber development and fiber quality traits. To determine when and how much of the GUS gene is expressed in cotton fiber cell, total RNA in each of the harvested fiber tissues will be isolated and quantitative RT-PCR will be performed. The results will reveal the dynamic changes of GUS gene and gene product in fiber tissues of cotton plants grown under different irrigation levels throughout the sampling period (10, 14, 17, 19, 21, 24, and 27 dpa). At the same time, the structural and cell wall composition changes in fiber over the sampling time will be analyzed using FTIR and TGA technology at FBRI-TTU. Thirty FTIR spectra per sample will be acquired for each developmental stage. The correlation between structural and composition changes and molecular and biochemical changes (mentioned above) in fiber will be analyzed firstly for cotton plants grown under each irrigation level. Second, the association of dynamic changes of these traits with different levels of drought stress will be analyzed. The difference in these dynamic changes between drought-stressed and well-watered cotton plants will indicate the effects of drought stress on fiber development during secondary cell wall deposition and maturation processes. The correlation of drought stress with traits related to fiber quality and yield will be analyzed statistically. and cotton fiber quality and yield triats that are being mostly affected by field drought stress will be identified.
3. Progress Report:
In 2012, 4 CesA1-GUS transgenic cotton lines were planted at USDA-ARS-CSRL location for the 2nd year, with 3 different irrigation levels (well-watered, deficit irrigation 33%, and dryland cotton) with 3 replicates per condition. Cotton flowers were tagged daily as they opened for about 5 weeks, and cotton bolls at set DPA were collected and fiber tissues harvested. GUS report gene activities in fiber tissues were quantitatively determined by fluorometric analysis. The pattern of CesA1 gene expression during secondary cell wall deposition phase of fiber development was examined. The fiber structural changes within fiber cells over time were analyzed using FTIR technology and microscopically at FBRI-TTU. The results from reporter gene GUS activity analysis showed that cellulose production in fibers of drought-stressed plants starts, peaks, and ends much earlier than in those of well-watered plants. As a result, the phases of fiber cell elongation and secondary cell wall synthesis were shortened for cottons under drought stress. Results from fiber structural and composition analyses showed that fibers of drought-stressed plants matured much faster than those of well-watered plants. The drought-caused changes in cellulose production in fiber tissues are tightly correlated with the changes in the speed of secondary cell wall deposition and maturity of fiber cells under drought. Fiber analysis results show drought stress significantly reduced fiber quality such as fiber length, fiber elongation, and fiber strength. Fibers produced under drought had more immature fibers and were less uniform than those produced under well-watered condition. The study also shows that drought causes significant yield loss by reducing plant size, boll set, boll size, and seed number per boll. The results of this study indicate that cellulose production in fiber tissues is very sensitive to drought stress. The timing, amount, and duration of cellulose production during secondary cell wall synthesis of fiber cells are closely associated with fiber quality traits, such as fiber elongation, fiber length, fiber maturity, and fiber uniformity. Molecular modification of regulatory processes for cellulose production of cotton fibers in response to drought stress could lead to the improvement of fiber quality traits for cotton plants grown under dryland and/or drought-stressed conditions.