Plastome Phylogenomic and Biogeographical Study on Thuja (Cupressaceae)

Functional Characterization of the PoWHY1 Gene from Platycladus orientalis and Its Role in Abiotic Stress Tolerance in Transgenic Arabidopsis thaliana

The frequent occurrence of extreme weather conditions in the world has brought many unfavorable factors to plant growth, causing the growth and development of plants to be hindered and even leading to plant death, with abiotic stress hindering the growth and metabolism of plants due to severe uncontrollability. The WHY1 transcription factor plays a critical role in regulating gene expression in plants, influencing chlorophyll biosynthesis, plant growth, and development, as well as responses to environmental stresses. The important role of the PoWHY1 gene in regulating plant growth and adaptation to environmental stress has become a hot research topic. However, the mechanism of the PoWHY1 gene in Platycladus orientalis under abiotic stress is still unclear. Here, the PoWHY1 gene was analyzed bioinformatically using P. orientalis as study material, and the role of the gene against abiotic stress conditions in Arabidopsis thaliana was verified using transgenic technology. It was found that overexpression of PoWHY1 increased seed germination, decreased malondialdehyde accumulation, increased proline content, and delayed the senescence process under salt stress. The expression levels of JAZ1, LOX1, ABI1, and ABI2 were decreased, while the expression levels of RAB18, APX1, GSTF6, and DREB2A were increased, indicating that overexpression of PoWHY1 enhanced the salt stress tolerance of A. thaliana. Furthermore, PoWHY1 overexpression also increased drought tolerance in A. thaliana. From the above results, it can be concluded that maintaining high PoWHY1 expression levels in the leaves of P. orientalis can improve their environmental adaptability. The results provide a scientific basis for understanding the gene function of the PoWHY1 gene of P. orientalis under stress conditions and lay the foundation for further research on the function of the PoWHY1 gene.

Seeing through the hedge: Phylogenomics of Thuja (Cupressaceae) reveals prominent incomplete lineage sorting and ancient introgression for Tertiary relict flora

The Eastern Asia (EA) - North America (NA) disjunction is a well-known biogeographic pattern of the Tertiary relict flora; however, few studies have investigated the evolutionary history of this disjunction using a phylogenomic approach. Here, we used 2369 single copy nuclear genes and nearly full plastomes to reconstruct the evolutionary history of the small Tertiary relict genus Thuja, which consists of five disjunctly distributed species. The nuclear species tree strongly supported an EA clade Thuja standishii-Thuja sutchuenensis and a "disjunct clade", where western NA species T. plicata is sister to an EA-eastern NA disjunct Thuja occidentalis-Thuja koraiensis group. Our results suggested that the observed topological discordance among the gene trees as well as the cytonuclear discordance is mainly due to incomplete lineage sorting, probably facilitated by the fast diversification of Thuja around the Early Miocene and the large effective population sizes of ancestral lineages. Furthermore, approximately 20% of the T. sutchuenensis nuclear genome is derived from an unknown ancestral lineage of Thuja, which might explain the close resemblance of its cone morphology to that of an ancient fossil species. Overall, our study demonstrates that single genes may not resolve interspecific relationships for disjunct taxa, and that more reliable results will come from hundreds or thousands of loci, revealing a more complex evolutionary history. This will steadily improve our understanding of their origin and evolution.

Genetic Diversity and Population Genetic Structure of Ancient Platycladus orientalis L. (Cupressaceae) in the Middle Reaches of the Yellow River by Chloroplast Microsatellite Markers

Ancient trees are famous for their life spans of hundreds or even thousands of years. These trees are rare, a testament to history and are important for scientific research. Platycladus orientalis, with the longest life span and a beautiful trunk, has become the most widely planted tree species and is believed to be sacred in China. Extensive declines in habitat area and quality pose the greatest threats to the loss of genetic diversity of ancient P. orientalis trees in the middle reaches of the Yellow River. Strengthening the protection of P. orientalis genetic resources is of great significance for the long-term development of reasonable conservation and breeding strategies. To better understand the genetic diversity and population structure of P. orientalis, we successfully analyzed four polymorphic chloroplast simple sequence repeat (cpSSR) loci and applied them to diversity and population structure analyses of 202 individuals from 13 populations in the middle reaches of the Yellow River. Based on the cpSSR data, 16 alleles were detected across 202 individuals, and a moderate level of genetic diversity was inferred from the genetic diversity parameters (H = 0.367 and AR = 1.964). The mean pairwise genetic differentiation coefficient (Fst) between populations was 0.153, indicating relatively high genetic population differentiations. Analysis of molecular variance (AMOVA) showed that only 8% of the variation occurred among populations. Structure analysis divided the 13 P. orientalis populations into two groups with no significant geographic population structure, which was consistent with the unweighted pair group method with arithmetic mean (UPGMA) and Mantel test results. These results may indicate that transplanting and cultivation by ancient human activities are the main factors responsible for the revealed pattern of genetic differentiation of ancient P. orientalis populations. Our research is of great significance for the future establishment of protection schemes and scientific breeding of P. orientalis.