Gene Mapping And Photosynthetic Physiological Analysis Of A New Sub-red Mutant In Upland Cotton

A sub-red mutant, a new qualitative trait mutant in upland cotton with high photosynthesis efficiency, has been regarded as a potentially elite germplasm. Molecular markers linked to sub-red mutant gene are of great importance to fine mapping and cloning of the sub-red gene. In this research, one BC1 population (PD-17×GK19) was used to map the sub-red gene by microsatellite (SSR) and sequence-related amplified polymorphism (SRAP). Meanwhile, combining the molecular marker with the morphological characters to set up integrating map can integrate the classical genetic research with the molecular genetic research. Furthermore, the study on the contain change of photosynthesis pigments such as chlorophyll, carotenoid and anthocyanin at various stages, would open out the mechanism of enduring the strong light and high photosynthesis efficiency.419 SSR and 238 SRAP primers, covering all the identified chromosomes and most linkage groups of cotton, were screened in BC1 populations by bulked segregation analysis (BSA). Linkage analysis and part molecular linkage map of sub-red mutational gene (tentatively named as Rs) was constructed with MAPMAKER. The results showed that Rs gene is located between NAU1362 and melem6. The other 7 markers linked to Rs were CIR393-160, CIR393-200, CIR335, NAU1048, BNL2634, BNL1597 and me5em5.The linkage map covered 70.5 CM, and the most adjacent marker linked to Rs was emlem6, with a genetic distance of 8.3 CM. Based on the known genetic map of tetraploid cotton, the Rs gene is located on the cotton chromosome 7.The content of photosynthetic pigments and anthocyanin in the leaves of mutant, the normal green plant and their F1 was determined at various stages. The result showed that the photosynthetic pigments were not significantly different, so the mutant did result from to the photosynthetic pigment defect type. However, the anthocyanin content of sub-red mutant exceeded that of the wild type to a great extent, thus the mutant should be categorized into the anthocyanin mutant type.The steady-state mRNA levels of CHS, F3H and DFR genes, which controll the anthocyanin synthesis in sub-red mutant, normal green plant and classical red plant, were examined by RT-PCR. The expression analysis indicated that these genes can be expressed in three types, with some difference in expression levels. However, so it might be deduced that the up genes of anthocyanin synthesis path, which were of different expression levels, resulted in the difference in the structure gene level expression.That sub-red mutant has better photosynthesis efficiency than normal green plant under strong light. This might be attributed to the fact that the anthocyanin can protect chloroplast from light stress and consequently enhance the photosynthesis efficiency.