Abstract
BackgroundCotton fiber maturity is an important factor for determining the commercial value of cotton. How fiber cell wall development affects fiber maturity is not well understood. A comparison of fiber cross-sections showed that an immature fiber (im) mutant had lower fiber maturity than its near isogenic wild type, Texas marker-1 (TM-1). The availability of the im mutant and TM-1 provides a unique way to determine molecular mechanisms regulating cotton fiber maturity.ResultsTranscriptome analysis showed that the differentially expressed genes (DEGs) in the im mutant fibers grown under normal stress conditions were similar to those in wild type cotton fibers grown under severe stress conditions. The majority of these DEGs in the im mutant were related to stress responses and cellular respiration. Stress is known to reduce the activity of a classical respiration pathway responsible for energy production and reactive oxygen species (ROS) accumulation. Both energy productions and ROS levels in the im mutant fibers are expected to be reduced if the im mutant is associated with stress responses. In accord with the prediction, the transcriptome profiles of the im mutant showed the same alteration of transcriptional regulation that happened in energy deprived plants in which expressions of genes associated with cell growth processes were reduced whereas expressions of genes associated with recycling and transporting processes were elevated. We confirmed that ROS production in developing fibers from the im mutant was lower than that from the wild type. The lower production of ROS in the im mutant fibers might result from the elevated levels of alternative respiration induced by stress.ConclusionThe low degree of fiber cell wall thickness of the im mutant fibers is associated with deregulation of the genes involved in stress responses and cellular respiration. The reduction of ROS levels and up-regulation of the genes involved in alternative respirations suggest that energy deprivation may occur in the im mutant fibers.
Highlights
Cotton fiber maturity is an important factor for determining the commercial value of cotton
When the microarray results from the im mutant fibers are compared with the results from the wild type cottons stressed by drought or salt using a 2 fold difference criterion (p value ≤ 0.05), we found that 624 Differentially expressed gene (DEG) (72%) and 236 DEGs (27%) of the 867 DEGs identified in the im mutant fibers overlapped the DEGs in the drought stressed cotton fibers and the salt stressed cotton roots, respectively (Figure 8)
Based on the results from microarray comparison of the cotton im mutant to a near isogenic wild type, we identified differentially expressed genes in developing fibers of the im mutant that are consistent with the loss of secondary cell wall in the mutant (Figure 9)
Summary
Cotton fiber maturity is an important factor for determining the commercial value of cotton. Fiber quality is classified based on its physical properties such as length, strength, fineness, and maturity [1,2]. To measure fiber maturity and fineness, cell wall area (A) and perimeter (P) of multiple fibers need to be measured using the microscopic images from fiber cross-sections [2,3]. Absolute value of fiber maturity defined as circularity (θ) representing the degree of fiber cell wall development is calculated using the equation, θ = 4πA/P2 [2,3,4]. Textile industry and agricultural marketing services have used the MIC values as a key quality assessment parameter of determining the fiber maturity [1,2]. Water content of soil, and mineral nutrition significantly affect the MIC values of cotton fibers: environmental factors affect MIC value of cotton fibers [1,2,3,4,5]
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