Development and characterization of a large mutant population of a rice variety Katy for functional genomics studies and breeding

Authors: Jia, Yulin; WANG, ZHONGHUA - Zhejiang Wanli University; Jia, Melissa; RUTGER, J - Retired ARS Employee; MOLDENHAUER, KAREN - University Of Arkansas

Submitted to: Crop Breeding, Genetics and Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2019
Publication Date: 8/19/2019
Citation: Jia, Y., Wang, Z., Jia, M.H., Rutger, J.N., Moldenhauer, K. 2019. Development and characterization of a large mutant population of a rice variety Katy for functional genomics studies and breeding. Crop Breeding, Genetics and Genomics. https://doi.org/10.20900/cbgg20190014.
DOI: https://doi.org/10.20900/cbgg20190014

Interpretive Summary: Katy is a long grain tropical japonica variety that is important for disease resistance studies and studies of the rice genome. One method of studying the rice genome involves applying a chemical or physical mutagen to rice seeds, which causes genetic variation to occur, and allows scientists to select and observe the functions of genes. Here, a Katy mutant population consisting of 23,558 lines was created and evaluated under controlled conditions using the three most prevalent mutagens in rice genomic studies at varying rates and concentrations: the chemical mutagen ethyl methane sulfonate and the physical mutagens fast neutron and 60-Cobalt gamma radiation. The ability of each mutagen at each different concentration to produce mutations in the plants were evaluated by determining whether a plant had an inhibited ability to produce chlorophyll due to mutations through observing the color of the plant seedlings. These lines were evaluated at the third and fifth generation of the plants assuming the seeds directly applied with mutagens are the first generation. It was discovered that ethyl methane sulfonate at the highest concentration, 1.2%, produced the most chlorophyll deficiency mutations in both generations. However, all mutagens produced mutations indicating that the developed population will be useful for future rice genomic studies.

Technical Abstract: The availability of a large mutant population is an important genetic resource for functional genomic studies and breeding. Katy, a publicly available long grain tropical japonica rice variety with an excellent package of disease resistance and suitable agronomic traits, was used to develop a large mutant population. A combination of ethyl methane sulfonate (EMS), fast neutron (FN), and gamma irradiation (60Co) treatments were applied at varying dosages to develop the population. Approximately 7,500 rice seeds were each treated with EMS (0.4%, 0.8%, and 1.2%) and 60Co (200 GY), and approximately 10,000 rice seeds were exposed to 7.7 GY, 26.3 GY, and 49.4 GY dosages of FN. Mutation rates were initially evaluated at the M2 generation by assessing chlorophyll biosynthesis deficiencies. The mutation rates of each line were detected at 1.04% for 0.4% EMS, 5.04% for 0.8% and 1.2% EMS, 2.9% for 26.3 GY FN, 3.2% for 49.4 GY FN, and 5.04% for 60Co 200 GY for the M2 population. After seeds were advanced to M4 using a single seed breeding strategy, the genotype identity of 189 randomly selected lines was verified with nine simple sequence repeat markers and 96 randomly selected lines were evaluated for mutant morphological phenotypes. The analysis uncovered slightly higher frequencies of morphological mutants at M4 than was observed in the M2 generation. The highest percentage of morphological mutants were observed in the populations treated with 1.2% EMS suggesting that this concentration of EMS was the most effective mutagen in these studies. These findings suggest that the Katy putative mutant population consisting of 23,558 individuals is a potential asset for rice functional genomics studies and breeding.