J Syst Evol

• Research Article •    

Functional significance of asymmetrical retention of parental alleles in a hybrid pine species complex

Chang Qu1, Hong‐Na Kao1, Hui Xu1, Bao‐Sheng Wang2, Zhi‐Ling Yang3, Qi Yang4, Gui‐Feng Liu1, Xiao‐Ru Wang5, Yan‐Jing Liu1*, and Qing‐Yin Zeng1*   

  1. 1 State Key Laboratory of Tree Genetics and Breeding, Chinese Academy of Forestry and Northeast Forestry University, Beijing 100091, China;
    2 Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China;
    3 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Yunnan 666303, China;
    4 State Key Laboratory of Subtropical Silviculture, College of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou, Zhejiang 311300, China;
    5 Department of Ecology and Environmental Science, UPSC, Umeå University, SE-90187 Umeå, Sweden
    *Authors for correspondence. Yan‐Jing Liu. E‐mail: yan.jing.liu@163.com; Qing‐Yin Zeng. E‐mail: qingyin.zeng@caf.ac.cn
  • Received:2022-12-27 Accepted:2023-03-03 Online:2023-05-04

Abstract: Hybrid genomes usually harbor asymmetrical parental contributions. However, it is challenging to infer the functional significance of asymmetrical retention of parental alleles in hybrid populations of conifer trees. Here we investigated the diversity in the glutathione S-transferase (GST) gene family in a hybrid pine Pinus densata and its parents (Pinus tabuliformis and Pinus yunnanensis). Plant GSTs play major roles in protecting plants against biotic and abiotic stresses. In this study, 19 orthologous groups of GST genes were identified and cloned from these three species. We examined their expression in different tissues, and then purified the corresponding proteins to characterize their enzymatic activities and specificities toward different substrates. We found that among the 19 GST orthologous groups, divergence in gene expression and in enzymatic activities toward different substrates was prevalent. P. densata preferentially retained P. yunnanensis-like GSTs for 17 out of the 19 gene loci. We determined the first GST crystal structure from conifer species at a resolution of 2.19??. Based on this structure, we performed site-directed mutagenesis to replace amino acid residuals in different wild-types of GSTs to understand their functional impacts. Reciprocal replacement of amino acid residuals in native GSTs of P. densata and P. tabuliformis demonstrated significant changes in enzyme functions and identified key sites controlling GSTs activities. This study illustrates an approach to evaluating the functional significance of sequence variations in conifer genomes. Our study also sheds light on plausible mechanisms for controlling the selective retention of parental alleles in the P. densata genome.

Key words: enzymatic function, functional divergence, gene expression, glutathione S‐transferases, homoploid hybrid species