Project Summaries

12-199  Project Manager: D. C. Jones

STRUCTURAL AND FUNCTIONAL GENOMIC ANALYSIS OF THE IMMATURE-1 GENE THAT CONTROLS COTTON FIBER FINENESS AND MATURITY

Hee Jin Kim, USDA-ARS

We proposed to perform the following five itemized sub-projects: 1) analyze and compare fiber properties of developing cotton fibers from TM-1 and im mutant, 2) evaluate fiber properties from each one of 368 F2 plants to determine the genetic control of immature fiber, 3) extract genomic DNAs from each one of F2 progeny plants, 4) identify molecular markers associated with the im genetic locus, and 5) isolate high quality of RNAs from developing cotton fibers of TM-1 and im. All of the planned research have been completed. The outcomes from the research project have generated two manuscripts. The results of fiber properties and mapping data have been published in Theoretical and Applied Genetics (Kim et al. 2013), and the fiber maturity data measured by Cottonscope will be published in Textile Research Journal (Rodgers et al. accepted).

To understand molecular mechanisms of fiber maturity and fineness responsible for the quality of fibers and yarns, two near isogenic cotton lines (TM-1 and im mutant) showing significant difference of micronaire were compared. Fiber property measurements obtained by HVI showed that the micronaire value of im mutant fibers was 37% lower than that of TM-1 fibers. Little differences of fiber length (UHML) and uniformity were detected between TM-1 and mutant line, whereas a detectable reduction (7.2 %) of fiber strength was observed in im mutant fibers as compared to TM-1 fibers. The comparisons of fiber properties measured by AFIS showed little difference in fiber length (UQL and Lw) between two NILs, but statistically significant reductions of fineness (5.9 %) and maturity ratio (5.0 %) of im mutant fibers. The low MIC value and maturity ratio of im mutant fibers indicated that mutant fibers were less mature than TM-1 fibers.

Fiber maturity refers to mean degree of fiber cell wall thickening relative to the perimeter of effective diameter of the fiber. The differences of fiber maturity between two NILs were determined by microscopic image analyses of thin sections of fiber bundles. Image analysis of cross-sectioned fibers showed that the cell wall area of most cross-sectioned im mutant fibers was thinner than that of TM-1 fibers. The cell wall area (A) and perimeters (P) of individual fiber sections from multiple microscopic images were measured to determine the circularity (θ) referring degree of fiber cell wall thickening. There was a very little but detectable difference (4.56 %) of the average perimeter size of individual fiber between im mutant (51.5 µm) and TM-1 (53.8 µm), but there was significant difference (37.7 %) of average cell wall area excluding lumen (vacuole) area between im mutant (70.1 µm2) and TM-1 (112.4 µm2). The circularity (θ) of im mutant fibers (0.37) was 26 % lower than that of TM-1 fibers (0.50). Based on these results, we concluded that the non-fluffy phenotype in im mutant was caused by the low degree of fiber cell wall thickening.

SSR markers from 366 F2 progeny were mapped using program JoinMap3.0 with LOD score C15.0, and the results were analyzed with the lint % and MIC value of F2 progeny. Thirteen SSR markers that were closely linked to the im gene were identified on chromosome 3.

When the fiber maturity of developing cotton fibers from TM-1 and im mutant was measured by Cottonscope, there were distinct differences of fiber maturity during fiber development between TM-1 and im. The Cottonscope maturity pattern of developing im fibers was lower than that of developing TM-1 fibers and in accordance with the lower circularity of mature fibers of im mutant over its NIL, TM-1. As fiber cell wall was thickening during fiber development (from 24 DPA to mature fiber), the maturity of each NIL was higher with increasing DPA. Total RNAs were extracted from developing cotton fibers (10, 17, and 28 DPA) of TM-1 and im mutant and the quality was measured with Agilent bioanalyzer. All of the extracted RNAs had high RIN numbers that are eligible to be used for microarray and RNA-seq.

 

Project Year: 2012
 

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