Pistacia chinensis Bunge (P. chinensis), a dioecious plant species, has been widely found in China. The female P. chinensis plants are more important than male plants in agricultural production, as their seeds can serve as an ideal feedstock for biodiesel. However, the sex of P. chinensis plants is hard to distinguish during the seedling stage due to the scarcity of available transcriptomic and genomic information. In this work, Illumina paired-end RNA sequencing assay was conducted to unravel the transcriptomic profiles of female and male P. chinensis flower buds. In total, 50,925,088 and 51,470,578 clean reads were obtained from the female and male cDNA libraries, respectively. After quality checks and de novo assembly, a total of 83,370 unigenes with a mean length of 1.3 kb were screened. Overall, 64,539 unigenes (77.48%) could be matched in at least one of the NR, NT, Swiss-Prot, COG, KEGG, and GO databases, 71 of which were putatively related to the floral development of P. chinensis. Additionally, 21,662 simple sequence repeat (SSR) motifs were identified in 17,028 unigenes of P. chinensis, and the mononucleotide motif was the most dominant type of repeats (52.59%) in P. chinensis, followed by dinucleotide (22.29%), trinucleotide (20.15%). The most abundant repeats were AG/CT (13.97%), followed by AAC/GTT (6.75%) and AT/TA (6.10%). Based on these SSR, 983 EST-SSR primers were designed, 151 of which were randomly chosen for validation. Of these validated EST-SSR markers, 25 SSR markers were found to be polymorphic between male and female plants. One SSR marker, namelyPCSSR55, displayed excellent specificity in female plants, which could clearly distinguish between male and female P. chinensis. Altogether, our findings not only reveal that the EST-SSR marker is extremely effective in distinguishing between male and female P. chinensis but also provide a solid framework for sex determination of plant seedlings.

Comparing gene expression among parasitic plants infecting different host species can have significant implications for understanding host-parasite interactions. Taxillus nigrans is a common hemiparasitic species in Southwest China that parasitizes a variety of host species. However, a lack of nucleotide sequence data to date has hindered transcriptome-level research on T. nigrans. In this study, the transcriptomes of T. nigrans individuals parasitizing four typical host species (Broussonetia papyrifera [Bpap] a broad-leaved tree species; Cryptomeria fortunei [Cfor] a coniferous tree species; Cinnamomum septentrionale [Csep] an evergreen tree species; and Ginkgo biloba [Gbil] a deciduous-coniferous tree species) were sequenced, and the expression profiles and metabolic pathways compared among hosts. A total of 40.06 Gb of clean sequence data were generated in nine cDNA libraries. These were de novo assembled into 293,823 transcripts with an N50 value of 1790 bp. A large number of differentially expressed genes (DEGs) were identified when comparing T. nigrans individuals on different host species: Bpap vs. Cfor (713 DEGs), Bpap vs. Csep (1219), Bpap vs. Gbil (1514), Cfor vs. Csep (1639), Cfor vs. Gbil (1722), and Csep vs. Gbil (1723). Three hundred and eighty-one unigenes were common to all six pairwise comparisons; these were primarily associated with carbohydrate metabolism and energy metabolism, as determined in a KEGG enrichment analysis. Specific involvements included: the TCA cycle, biosynthesis of secondary metabolites, carbon metabolism, biosynthesis of amino acids and glyoxylate/dicarboxylate metabolism. A total of 251 unique unigenes were also identified, specific to either the Bpap vs. Cfor (249 unigenes) or Csep vs. Gbil (two unigenes) comparisons; partial unigenes were associated with the plasma membrane, response to endogenous stimuli, ion binding, and organic hydroxy compound metabolic processes. These results provide a foundation for further explorations of the detailed molecular mechanisms involved in plant parasitism.

Conifers make up about one third of global forests but are threatened by seed parasitoid wasp species. Many of these wasps belong to the genus Megastigmus, yet little is known about their genomic background. In this study, we provide chromosome‐level genome assemblies for two oligophagous conifer parasitoid species of Megastigmus, which represent the first two chromosome‐level genomes of the genus. The assembled genomes of Megastigmus duclouxiana and M. sabinae are 878.48 Mb (scaffold N50 of 215.60 Mb) and 812.98 Mb (scaffold N50 of 139.16 Mb), respectively, which are larger than the genome size of most hymenopterans due to the expansion of transposable elements. Expanded gene families highlight the difference in sensory‐related genes between the two species, reflecting the difference in their hosts. We further found that these two species have fewer family members but more single‐gene duplications than polyphagous congeners in the gene families of ATP‐binding cassette transporter (ABC), cytochrome P450 (P450) and olfactory receptors (OR). These findings shed light on the pattern of adaptation to a narrow spectrum of hosts in oligophagous parasitoids. Our findings suggest potential drivers underlying genome evolution and parasitism adaptation, and provide valuable resources for understanding the ecology, genetics and evolution of Megastigmus, as well as for the research and biological control of global conifer forest pests.