Light Deficiency Inhibits Growth by Affecting Photosynthesis Efficiency as well as JA and Ethylene Signaling in Endangered Plant Magnolia sinostellata

The endangered plant Magnolia sinostellata largely grows in the understory of forest and suffers light deficiency stress. It is generally recognized that the interaction between plant development and growth environment is intricate; however, the underlying molecular regulatory pathways by which light deficiency induced growth inhibition remain obscure. To understand the physiological and molecular mechanisms of plant response to shading caused light deficiency, we performed photosynthesis efficiency analysis and comparative transcriptome analysis in M. sinostellata leaves, which were subjected to shading treatments of different durations. Most of the parameters relevant to the photosynthesis systems were altered as the result of light deficiency treatment, which was also confirmed by the transcriptome analysis. Gene Ontology and KEGG pathway enrichment analyses illustrated that most of differential expression genes (DEGs) were enriched in photosynthesis-related pathways. Light deficiency may have accelerated leaf abscission by impacting the photosynthesis efficiency and hormone signaling. Further, shading could repress the expression of stress responsive transcription factors and R-genes, which confer disease resistance. This study provides valuable insight into light deficiency-induced molecular regulatory pathways in M. sinostellata and offers a theoretical basis for conservation and cultivation improvements of Magnolia and other endangered woody plants.

Identification of Potential Shade Response Regulators in Endangered Species Magnolia Sinostellata

Magnolia sinostellata is one of the endangered species in China and largely grows under canopy shade. However, the shade response molecular mechanism remains unclear. To explore potential regulators in the mechanism, weighted gene co-expression network analysis (WGCNA) was performed to analysis the trancriptome data of M. sinostellata leaves subjected to shading with different time. Gene co-expression analysis illustrated that lightsteelblue1, paleturquoise, darkolivegreen modules are closely associated with shade treatment. Gene ontology and KEGG analyses showed that genes in lightsteelblue1 module mostly participated in amino and nucleotide metabolism, genes in paleturquoise module mostly involved in carbon fixation and genes in darkolivegreen module mainly participated in photosynthesis related pathways. Through Cytoscape3.8.2, we identified 6, 7 and 8 hub genes in lightsteelblue1 module, paleturquoise module and darkolivegreen module, respectively. This study found that shading impacted photosynthesis, carbon assimilation and flowering of M. sinostellata. In addition, key shade response regulators identified in this study have laid a firm foundation for further investigation of shade response molecular mechanism and protection of shade sensitive plants.

Magnolia sinostellata and relatives (Magnoliaceae)

Magnolia sinostellata has been considered a synonym of Magnolia stellata by several taxonomists due to many shared morphological characters. With similar leaves and twigs, Magnolia amoena is distributed in areas near M. sinostellata. These three species were studied by comparing morphological, cytological and palynological characters, creating a maximum parsimony phylogenetic tree based on plastid DNA sequences and studying these taxa in the field. The results are as follows: M. sinostellata is a diploid, 2n=2x=38, and there are heterozygotes with paracentric inversion chromosomes in wild populations. Magnolia stellata is also a diploid, and there are heterozygotes with pericentric inversion chromosomes in wild populations. The abnormal chromosome behaviour in meiosis has serious effects on survival of the two species. Magnolia amoena is diploid with more or less normal meiosis except for a few lagging chromosomes in anaphase I and II. Magnolia stellata has a more complicated exine sculpture than the other two; exine structure is different in all three species. Separate species status for M. sinostellata is also supported by results of the plastid DNA phylogenetic study. Distributions, population descriptions and observations are provided, and based on all the evidence presented we conclude that M. sinostellata is a distinct species in M. subgenus Yulania.