Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2013
Publication Date: December 17, 2013
Citation: Kim, H.J., Tang, Y., Moon, H.S., Delhom, C.D., Fang, D.D. 2013. Functional analyses of cotton (Gossypium hirsutum L.) immature fiber (im) mutant reveal that fiber cell wall development is associated with sensitivity to stress. Biomed Central (BMC) Genomics. 14:889. Interpretive Summary: Cotton fiber quality is classified based on its physical properties. Among these properties, the fiber maturity referring to the degree of fiber cell wall development is least defined and understood. A wild type Upland cotton cultivar grown under normal environmental conditions produced fluffy cotton bolls with normal and thick cell wall development. The same cultivar could produce non-fluffy bolls with thin cell wall development when grown under severe stresses caused by drought, cold temperature, or pathogens. In contrast, immature fiber (im) mutant had non-fluffy bolls with extremely thin cell walls when it was grown under a regular field condition that had little or no obvious stresses from environments or pathogens. The im mutant and its near isogenic line wild type cotton provided a unique way to study molecular mechanisms regulating cotton fiber wall development that is an important factor for determining commercial value of cotton. Comprehensive comparisons between wild type cotton and im mutant using genomics analyses, fiber properties, and biochemical assays revealed that the im mutant is highly sensitive to stress so the gene expression patterns of the im mutant are significantly similar to those of cotton plants grown under stress conditions caused by severe weather or pathogens. For fiber cells to respond to the stress that the im mutant recognized in a highly sensitive manner, cell growth process in the im mutant was reduced. As results, the im mutant showed reduced fiber wall development that decreased its commercial value. The results provide an insight on molecular mechanisms that were regulated by stresses caused by environmental factors and regulate fiber maturity. Thus, the ability to manipulate the expression of genes regulating fiber maturity may lead to strategies for improving cotton fiber quality.
Technical Abstract: Background: Cotton fiber maturity refers the degree of fiber cell wall development and is an important factor for determining commercial value of cotton. The molecular mechanism regulating the fiber cell wall development has not been well characterized. Microscopic image analysis of the cross-sections of the immature fiber (im) mutant fibers grown under normal conditions with little stress showed low degree of fiber cell wall development. Similar phenomenon was usually found in wild type cotton fibers grown under stress conditions caused by severe weather or pathogens. The im mutant and its near isogenic line wild type Texas marker-1 (TM-1) provided a unique way to study molecular mechanisms regulating cotton fiber maturity. Results: Transcriptome analysis revealed that the differentially expressed genes identified from the im mutant fibers were significantly overlapped to those recently identified from wild type cotton fibers grown under abiotic stresses. Gene ontology enrichment analyses identified stress response and cellular respiration process governing the differential expressions in the im mutant fibers. Biochemical analyses showed that the reactive oxygen species (ROS) levels of developing fibers from im mutant were lower than those from TM-1 fibers. The lower levels of ROS in im mutant fibers might result from the elevated levels of alternative respiration induced by stress, and consequently, cause energy deprivation in the im mutant. Furthermore, transcriptome data in the im mutant fibers also showed the energy deprivation symptoms such as reduced levels of cell growth process (cell wall biosynthesis, protein synthesis, and sucrose metabolism) and elevated levels of the recycling process (starch degradation, transports, and metal ion binding). Conclusion: Comprehensive functional analyses showed that the low degree of fiber cell wall development of the im mutant fibers was associated with sensitivity to stresses. The results provide insight into how the molecular mechanisms affected by sensitivity to stresses regulate cotton fiber maturity.