Darwin’s Theory Of Evolution Meets Genetics And Genomics

Ching-Chu Yen^1,2*

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

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ABSTRACT – DOI: https://dx.doi.org/10.47204/EBR.2.1.2021.021-027

Plants have developed into two categories in the process of adapting to the evolution of salt stress. One type of halophytes can tolerate high salinity, with a salt tolerance range of 300-500 mM; the other type of glycophytes are more sensitive to salt, with a salt tolerance of 100-200 mM^[23]. Most of the crops belong to glycophytes, which are more sensitive to salinity, and rice is the most sensitive crop to salinity. Salt stress causes growth inhibition, yield reduction and poor quality of rice plants, and even plant deaths^[3,7]. Even for salt-tolerant rice varieties, Nona Bokra and Pokkali, which are recognized worldwide, when treated with 200 mM or 250 mM NaCl, the growth of Nona Bokra is obviously inhibited, and Pokkali is dead^[35,36]. In my research^[35,36], the salt-tolerance screening was performed by treating with 300 mM NaCl for 3 days. The parents of SM61 and all mutagenized lines died, and only SM61 survived. The parent, TNG67, was mutagenized with a chemical mutagen, NaN3 to produce CNY911303, and CNY911303 was mutagenized with a chemical mutagen, EMS to produce all mutagenized lines. SM61 is the mutagenic line obtained in this way. EMS, a chemical mutagen, often causes point mutations in biological individuals. I grew 1005 mutated scented japonica rice lines to the seventh steady genetic generation, and treated the seedlings with six true leaves with 300 mM NaCl for three days. Only the salt-tolerant line, SM61, survived. Unless it is transgenic or genetically encoded rice, it can survive in an environment treated with 300 mM NaCl^[22]. However, SM61 is the only non-transgenic or non-genetically encoded rice that can survive in the presence of 300 mM NaCl. I obtained F₁, F₂ and F₃ populations from the cross between SM61 and a salt-susceptible indica variety, TCS17. After culture with 200 mM NaCl for five days, 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^[35,36]. The mutated salt-tolerance gene explained close to 100% of the total phenotypic variation, and was tightly linked to RM223 (marker) located on chromosome 8[35,36], which was different from the results of previous studies investigating the relationship of QTLs with salt tolerance^{[6,14,18,19,24,27,38]}. This is the first report of mapping tightly linked markers of a single dominant mutated salt-tolerance gene^[35,36]. In my studies^[35-37], genetic chi-square analysis showed that the salt-tolerant characteristic of SM61 was inherited by a single dominant gene; linkage analysis of phenotypes and genotypes found the linkage markers that explain 100% of salt-tolerance in SM61, which proved that it was indeed a single gene regulation that caused SM61 can survive in high salt stress, 300 mM NaCl. The implication is that glycophytes plants have mutations in the most critical salt-tolerant single gene, which can make glycophytes plants that are extremely sensitive to salinity become the same as high-salinity-tolerant halophytes plants that can survive at high-salinity stress, 300 mM NaCl. The major breakthrough in genetics and genomics of my research confirms Darwin’s theory of evolution.