Flower development and sexual dimorphism in Vernicia montana

The mu oil tree(Vernicia montana Lour.) is a dioecious species, but the genetic mechanisms underlying its phenotypic sexual dimorphism are unclear. In this study, we determined two pivotal phases of sex differentiation of mu oil tree via morphological and histological analyses of unisexual flowers:(Ⅰ) differentiation of male or female primordia to produce staminate flowers(SFs) or transient hermaphrodite flowers(HFs),and(Ⅱ) complete abortion of stamens in transient HFs to generate pistillate flowers(PFs). A total of 1621 sex-biased genes were identified by comparative transcriptome analysis which exhibited elevated rates of protein evolution than unbiased genes. The female-biased genes were enriched in the production of defense compounds while male-biased genes were focused on the production of viable pollens. Transcriptomebased analysis revealed that the differentially expressed genes(DEGs) between PFs and SFs in phase Ⅰ involved in abscisic acid(ABA), auxin(AUX), cytokinin(CK), ethylene(ET), and gibberellin(GA) biosynthesis and signaling showed higher expression levels in males than in females in general, whereas the DEGs involved in jasmonic acid(JA) and salicylic acid(SA) pathways displayed opposite expression patterns. Moreover,differentially expressed endogenous ABA, AUX, GAs, JA, and SA exhibited consistent biased expression patterns with the DEGs by UPLC-MSbased analysis. Exogenous application of an anti-ethylene plant growth regulator could promote the development of stamens in PFs and generated HFs. Comparative transcriptomic and hormonal analyses of PFs and SFs in phase Ⅱ indicated an increase in ET concentration when abortion of stamens in PFs occurred. This study suggested that phytohormones play key roles in sex dimorphism and ET may determine the development of stamens in PFs of mu oil tree, which provides an insight into plant sex differentiation mechanisms.

A chromosome-level genome assembly provides insights into Cornus wilsoniana evolution, oil biosynthesis, and floral bud development

Cornus wilsoniana W.is a woody oil plant with high oil content and strong hypolipidemic effects,making it a valuable species for medicinal,landscaping,and ecological purposes in China.To advance genetic research on this species,we employed PacBio together with Hi-C data to create a draft genome assembly for C.wilsoniana.Based on an 11-chromosome anchored chromosome-level assembly,the estimated genome size was determined to be 843.51 Mb.The N50 contig size and N50 scaffold size were calculated to be 4.49 and 78.00 Mb,respectively.Furthermore,30474 protein-coding genes were annotated.Comparative genomics analysis revealed that C.wilsoniana diverged from its closest species∼12.46 million years ago(Mya).Furthermore,the divergence between Cornaceae and Nyssaceae occurred>62.22 Mya.We also found evidence of whole-genome duplication events and whole-genome triplicationγ,occurring at∼44.90 and 115.86 Mya.We further inferred the origins of chromosomes,which sheds light on the complex evolutionary history of the karyotype of C.wilsoniana.Through transcriptional and metabolic analysis,we identified two FAD2 homologous genes that may play a crucial role in controlling the oleic to linoleic acid ratio.We further investigated the correlation between metabolites and genes and identified 33 MADS-TF homologous genes that may affect f lower morphology in C.wilsoniana.Overall,this study lays the groundwork for future research aimed at identifying the genetic basis of crucial traits in C.wilsoniana.