Evolution of the mating type gene pair and multiple sexes in Tetrahymena

Guanxiong Yan; Wentao Yang; Xiaojie Han; Kai Chen; Jie Xiong; Eileen P Hamilton; Eduardo Orias; Wei Miao

doi:10.1016/j.isci.2020.101950

Evolution of the mating type gene pair and multiple sexes in Tetrahymena

iScience. 2020 Dec 30;24(1):101950. doi: 10.1016/j.isci.2020.101950. eCollection 2021 Jan 22.

Authors

Guanxiong Yan^{1

2

3}, Wentao Yang^{1

2

3}, Xiaojie Han^{3

4}, Kai Chen^{1

3}, Jie Xiong^{1

3}, Eileen P Hamilton⁵, Eduardo Orias⁵, Wei Miao^{1

2

3

6}

Affiliations

¹ State Key Laboratory of Freshwater Ecology and Biotechnology, Wuhan 430072, China.
² University of Chinese Academy of Sciences, Beijing 100049, China.
³ Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
⁴ College of Fisheries and Life Science, Dalian Ocean University, Dalian 116023, China.
⁵ Department of Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
⁶ CAS Center for Excellence in Animal Evolution and Genetics, Kunming 650223, China.

Abstract

The multiple mating type system of the Ciliate Tetrahymena thermophila is a self/non-self recognition system, whose specificity resides in a head-to-head, functionally distinct pair of genes, MTA and MTB. We have now sequenced and analyzed these mating type genes in nine additional Tetrahymena species. We conclude that MTA and MTB are derived from a common ancestral gene and have co-evolved for at least ∼150 Myr. We show that T. shanghaiensis, a perpetual selfer (unisexual) species, has a single mating type gene pair, whose MTA and MTB genes likely have different mating type specificity. We document the recent replacement of a complete different set of mating type specificities for another, illustrating how quickly this can happen. We discuss how varying conditions of reproductive stress could result in evolutionary co-adaptations of MTA and MTB genes and changes in mating type determination mechanisms.

Keywords: Biological Sciences; Evolutionary Biology; Evolutionary Mechanisms; Evolutionary Processes; Phylogenetics; Phylogeny.