Tree age did not affect the leaf anatomical structure or ultrastructure of Platycladus orientalis L. (Cupressaceae)

Transcriptome and Metabolome Analyses of Leaves from Cutting Rejuvenation of Ancient Cinnamomum camphora

Rejuvenation refers to the transition from the state of mature to juvenile. Many ancient Cinnamomum camphora have aged and died due to climatic and anthropic factors. Vegetative propagation can protect valuable germplasm resources. In this study, a 2000-year-old ancient C. camphora and its 2-year-old cutting plantlets were selected as experimental materials. The results indicated that the number of leaves with palisade tissue (Pal) cell layers was different between samples, with two layers in the rejuvenated leaves (RLs) and one layer in the mature leaves (MLs) and young leaves (YLs). Indole-3-acetic acid (IAA), isopentenyladenine (iP) and isopentenyladenosine (iPR) concentrations were significantly higher in RLs than in MLs and YLs, but the abscisic acid (ABA) concentration was lower. Targeted metabolome analysis identified 293 differentially accumulated metabolites (DAMs). Meanwhile, a total of 5241 differentially expressed genes (DEGs) were identified by transcriptome sequencing. According to the KEGG analysis, there were seven important enriched pathways in the MLs, RLs and YLs, including plant hormone signal transduction (57 DEGs), plant-pathogen interaction (56 DEGs) and MAPK signaling pathway-plant (36 DEGs). KEGG enrichment conjoint analyses of DEGs and DAMs identified 16 common pathways. Integrated analyses of cytological, hormone, metabolome and transcriptome elements can provide a research basis in regard to the rejuvenation regulatory mechanism of ancient C. camphora.

Morphological change and genome-wide transcript analysis of Haloxylon ammodendron leaf development reveals morphological characteristics and genes associated with the different C3 and C4 photosynthetic metabolic pathways

C4 photosynthesis outperforms C3 photosynthesis in natural ecosystems by maintaining a high photosynthetic rate and affording higher water-use and nitrogen-use efficiencies. C4 plants can survive in environments with poor living conditions, such as high temperatures and arid regions, and will be crucial to ecological and agricultural security in the face of global climate change in the future. However, the genetic architecture of C4 photosynthesis remains largely unclear, especially the genetic regulation of C4 Kranz anatomy. Haloxylon ammodendron is an important afforestation tree species and a valuable C4 wood plant in the desert region. The unique characteristic of H. ammodendron is that, during the seedling stage, it utilizes C3 photosynthesis, while in mature assimilating shoots (maAS), it switches to the C4 pathway. This makes an exceptional opportunity for studying the development of the C4 Kranz anatomy and metabolic pathways within individual plants (identical genome). To provide broader insight into the regulation of Kranz anatomy and non-Kranz leaves of the C4 plant H. ammodendron, carbon isotope values, anatomical sections and transcriptome analyses were used to better understand the molecular and cellular processes related to the development of C4 Kranz anatomy. This study revealed that H. ammodendron conducts C3 in the cotyledon before it switches to C4 in AS. However, the switching requires a developmental process. Stable carbon isotope discrimination measurements on three different developmental stages showed that young AS have a C3-like δ13C even though C4 Kranz anatomy is found, which is inconsistent with the anatomical findings. A C4-like δ13C can be measured in AS until they are mature. The expression analysis of C4 key genes also showed that the maAS exhibited higher expression than the young AS. In addition, many genes that may be related to the development of Kranz anatomy were screened. Comparison of gene expression patterns with respect to anatomy during leaf ontogeny provided insight into the genetic features of Kranz anatomy. This study helps with our understanding of the development of Kranz anatomy and provides future directions for studies on key C4 regulatory genes.

Chemotaxonomic Variation in Volatile Component Contents in Ancient Platycladus orientalis Leaves with Different Tree Ages in Huangdi Mausoleum

To gain insight into the differences in the composition and volatile components content in ancient Platycladus orientalis leaves with different tree ages in Huangdi Mausoleum, the volatile components were identified by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. The volatile components were statistically analyzed by orthogonal partial least squares discriminant analysis and hierarchical cluster analysis, and the characteristic volatile components were screened. The results exhibited that a total of 72 volatile components were isolated and identified in 19 ancient Platycladus orientalis leaves with different tree ages, and 14 common volatile components were screened. Among them, the contents of α-pinene (6.40-16.76%), sabinene (1.11-7.29%), 3-carene (1.14-15.12%), terpinolene (2.17-4.95%), caryophyllene (8.04-13.53%), α-caryophyllene (7.34-14.41%), germacrene D (5.27-12.13%), (+)-Cedrol (2.34-11.30%) and α-terpinyl acetate (1.29-25.68%) were relatively higher (>1%), accounting for 83.40-87.61% of the total volatile components. Nineteen ancient Platycladus orientalis trees were clustered into three groups through the HCA method based on the 14 common volatile components content. Combined with the results of OPLS-DA analysis, (+)-cedrol, germacrene D, α-caryophyllene, α-terpinyl acetate, caryophyllene, β-myrcene, β-elemene and epiglobulol were the differential volatile components to distinguish ancient Platycladus orientalis with different tree ages. The results revealed that the composition of the volatile components in ancient Platycladus orientalis leaves with different tree ages was different, showing different aroma characteristics, which provided a theoretical reference for the differential development and application of volatile components in ancient Platycladus orientalis leaves.

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.