No abstract

Lindera glauca (Lauraceae) is an economically important East Asian forest tree characterized by a dioecy in China and apomixis in Japan. However, patterns of population genetic diversity and structure of this species remain unknown for this species due to a lack of efficient molecular markers. In this study, we employed Illumina sequencing to analyze the transcriptomes of the female and male flower buds of L. glauca. We retrieved 59,753 and 75,075 unigenes for the female and male buds, respectively. Based on sequence similarity, 44,379 (74.27 %) unigenes for the female and 45,414 (60.49 %) unigenes for the male were matched to public databases. We identified 11,127 putative differentially expressed genes between the female and male buds and 20,048 expressed sequence tag-simple sequence repeats (EST-SSRs). From 3147 primer pairs designed successfully, 120 were selected for validation of polymorphism, and 13 could reliably amplify polymorphic bands and exhibited moderate levels of genetic diversity (e.g., N = 4.42; H = 0.56) when surveyed across 96 individuals of altogether six L. glauca populations from China and Japan. One of the three population genetic clusters identified in China was fixed in Japan, suggesting a historical population bottleneck following island immigration. The present study has generated a wealth of transcriptome data for future functional genomic research focused on the variable reproductive system of L. glauca (dioecy, apomixis) as well as EST-SSR markers for population genetics studies and its intriguing evolutionary shift from dioecy to apomixis in the wake of island colonization.

Aim The historical circumstances promoting the transition from sexual to apomictic reproduction in dioecious plant species remain poorly understood. Here, we investigated the divergence and demographic history of Lindera glauca, a dioecious tree generally considered to be obligate sexual in China while comprising only females (apomicts) in Japan. Location East Asia (China and Japan). Taxon Lindera glauca (Lauraceae) Methods Samples from 42 populations were genotyped using chloroplast DNA and nuclear microsatellite (nSSR) loci to assess genetic diversity and structure. The nSSR genotypes were also used to detect the mode of reproduction in Chinese and Japanese populations, respectively. Approximate Bayesian Computation on nSSRs and palaeoclimatic niche models provided further insights into the evolutionary and population demographic history. Results Chinese L. glauca was found to harbour both sexual and asexual genotypes. Chinese and Japanese L. glauca underwent likely severe bottlenecks during a mid‐Pleistocene glacial period, possibly marking the split time of the island lineage from its mainland ancestor. In contrast to Chinese L. glauca, the Japanese lineage experienced a massive range contraction during the Last Glacial Maximum and postglacial expansions. Main Conclusions While reproductive assurance plays an important role in the selection of apomixis in Chinese L. glauca, the lack of male plants in Japan likely reflects population demographic history driven by (Late) Quaternary climate change. Hence, the present study demonstrates a possible link between palaeoclimate change and the transition to exclusively apomictic reproduction in a dioecious tree.

Cercidiphyllum, the only member of Cercidiphyllaceae, contains two extant species: Cercidiphyllum japonicum and Cercidiphyllum magnificum. Here, we reported their complete chloroplast genomes by de novo assembly. The chloroplast genome sizes of C. japonicum and C. magnificum were 159,871 and 159,899 bp, respectively. The two chloroplast genomes have 99.7% sequence identity and were highly conserved in GC content (37.9%), gene content (132 genes), and gene order. Phylogenetic analysis of the chloroplast genomes confirmed the monophyly of Cercidiphyllum and recovered Cercidiphyllaceae as a member of the 'woody clade' of Saxifragales.