Mendelian Genetics Meets Genomics – From QTLs To Single Gene

Ching-Chu Yen^1,2*

¹Yun-Lin County Dou-Nan Senior High School, (TAIWAN)
²No.212, Zhongshan Rd., Dounan Township, Yunlin County 63044, (TAIWAN)

PAGE NO: 15-20

ABSTRACT – DOI: https://dx.doi.org/10.47204/EBR.2.1.2021.015-020

All previous studies on gene regulation of salt tolerance and heat tolerance are based on multi-gene regulation, and no one has studied single-gene regulation in inheritance and linkage marker analyses. My research^[27-29] is the only study on salt tolerance and heat tolerance with single gene regulation, which is in full compliance with the Mendelian Law of Segregation and Law of Independent Assortment. The key reason why the previous multi-based control of salt-tolerance and heat-tolerance genes can be converted into single-gene regulation is to redefine what is meant by salt tolerance and heat tolerance. In my study of salt tolerance^[27,28], I adopt hydroponic culture medium to deducts soil interference factors, avoid high temperature to deduct heat stress interference, fixed plant growth stage, fixed salt concentration treatment and number of days for salt treatment. The rice platns at the six true-leaf stage were cultured in hydroponic culture medium containing 200 mM NaCl for 5 days at a mean temperature of 30/20°C (day/night), and then transferred to a hydroponic culture medium without NaCl and grown for 2 weeks. The survival plants (R) are defined as salt tolerance, and the unsurvival plants (S) are defined as salt sensitive. Morever, in my experiments on linkage analysis^[27-29], the plants were treated with 200 mM NaCl at a mean temperature of 35/25°C (day/night) for five days under non-shaded conditions during July and August, heat stress interference not deducted. The survival plants are defined as salt-heat tolerance, and the unsurvival plants are defined as non-salt-heat tolerance. Only my study was the survival or the unsurvival of plants as the judgment of salt tolerance and heat tolerance, divided into two parts, expressed in qualitative characters. Instead of using the traditional a continuous distribution of stress tolerance and stress susceptibility indices as the criterion for salt-tolerant and heat-tolerant traits, it is the key to the success of finding a 100% explanation of the single gene for salt-tolerance and heat-tolerance.

My studies^[27-29] were to analyze heritage characters and linkage markers of the screened japonica line, SM61, for a mutated salt-tolerance gene and the indica variety, TCS17, for a heat-tolerance gene by using F₁ and F₂ populations derived from a cross between a salt-tolerant and heat-susceptible japonica line, SM61, and a salt-susceptible and heat-tolerant indica variety, TCS17. SM61 and F1 (SM61×TCS17; TCS17×SM61) plants survived (R) while TCS17 plants did not (S). The R to S ratio in 513 F₂ plants showed a good fit to the Mendelian 3 : 1 segregation ratio by a Chi-square test indicating that the salt-tolerance of SM61 was governed by a single dominant gene (TABLE 1). The result conforms to the Mendelian Law of Segregation. I predicted that, the A genotypic percentage of the RM223 marker occupied 100 % of chromosome 8, the salt-tolerance of SM61 was governed by a single semidominant gene; the H and B genotypic percentage of the C61009 marker occupied 100 % of chromosome 4, the heat-tolerance of TCS17 was governed by a single dominant gene (TABLE 2). These were located on diffreent chromosomes. Chi-square values indicated that the F₂ population had good fits to a Mendelian 3 : 13 segregation ratio for homozygote-dominant salt-tolerant and dominant heat-tolerant (R) and non-homozygote-dominant salt-sensitive or recessive heat-sensitive (S) traits indicating that the salt-tolerance of SM61 was governed by a single homozygote-dominant gene and the heat-tolerance of TCS17 was governed by a single dominant gene (TABLE 3). The result conforms to the Mendelian Law of Independent Assortment. The salt-tolerance gene, ST8, which conferred the salt tolerance of SM61 was mapped on chromosome 8 flanked RM223 marker; the heat-tolerance gene, HT4, which conferred the heat tolerance of TCS17 was mapped on chromosome 4 flanked C61009 marker. My studies^[27-29] were therefore the first of mapping tightly linked markers of a single dominant mutated salt-tolerance gene in japonica line, SM61 and a single dominant heat-tolerance gene in indica variety, TCS17.