Studies On Flavonoid Oxidase Genes And Their Regulation To Fiber Coloration In Colored Cotton

Natural colored cotton becomes more and more attractive to textile industry because of their unique non-fading and environmentally friendly properties. The research about fiber color has been performed for many years. The pigment in colored cotton fiber was identified as flavonoids and various flavonoid genes were studied in previous studies. Flavonoid oxidation in plant is mainly catalyzed by polyphenol oxidases (catechol oxidases and laccases) and peroxidases. Therefore, we used brown cotton and green cotton as materials, and studied the relationship between the coloration and flavonoid oxidation. The main results were showed as below:1. The color of brown cotton fiber deepened obviously from 25 d. The activity of POD increased gradually from 15 d, and increased at a high rate of speed from 20 d to 30 d. While the change of CO activity was tiny after 20 d, and the CO activity was stable at a level. The content of flavonoids which could be measured in brown fiber declined continuously. The study showed that there was a close relationship between coloration and flavonoid oxidation which was catalyzed by POD in brown fiber. However, there was no clear evidence for CO participation in flavonoid oxidation. For green fiber, there was no change in color until 20 d. But the activity of POD was always at a lower level and the CO activity declined continuously. The content of flavonoids measured in green fiber was always at a higher level. It suggested that flavonoid oxidation in green cotton fiber was rare. The activity of LAC was not detected in the cotton fibers. After adding oxidation inhibitor (ascorbic acid) to the medium, the activity of enzymes and the coloration were significantly inhibited, and the growth and development of ovule and fiber were also highly affected.2. All LAC proteins of Arabidopsis were collected from TAIR. They were used as queries to carry out a genome-wide identification in upland cotton.48 LAC members were identified in upland cotton and they were divided into six subfamilies. Using the same method,134 POD members and 11 CO members were identified in upland cotton genome. The GhLACs were divided into five subfamilies and the GhCOs were into three. A further analysis of gene duplication events was performed by positioning the members on the chromosomes. It showed that the numbers of duplicate events in three gene families were less. So each gene family of upland cotton did not have a massive family amplification in the history of evolution.3. The qRT-PCR was conducted to analyze the expression level of genes selected from each gene family according to the classification of the subfamily. Results demonstrated that the differential expression of the genes were obvious among the three cotton lines. In addition, many POD genes in brown fiber always had a higher expression level during the period of coloration, but the expression levels were lower in green fiber. However, expression levels of LAC and CO genes in cotton fiber were relative low. The levels of LAC genes during the coloration were stable, while the levels of CO genes decreased continuously. The results mentioned above indicated that LAC and CO genes might be not crucial in oxidation of flavonoids in colored cotton, and the oxidation of pigment in brown cotton fiber was closely related to genes expression and enzyme activity of POD.