Gene Co-expression Network and Regression Analysis Identify the Transcriptomic, Physiological, and Biochemical Indicators of the Response of Alpine Woody Plant Rhododendron rex to Drought Stress.

Increasing severity of drought stress due to global change and extreme weather has been affecting the biodiversity, function, and stability of forest ecosystems. However, despite being an important component in the alpine and subalpine vegetation in forest ecosystems, Rhododendron species have been paid rare attention in the study of molecular mechanism of tolerance or response to drought. Herein, we investigated the correlation of transcriptomic changes with the physiological and biochemical indicators of Rhododendron rex under drought stress by using the co-expression network approach and regression analysis. Compared with the control treatment, the number of significantly differentially expressed unigenes (DEGs) increased with the degree of drought stress. The DEGs were mainly enriched in the cell wall metabolic process, signaling pathways, sugar metabolism, and nitrogen metabolism. Coupled analysis of the transcriptome, physiological, and biochemical parameters indicated that the metabolic pathways were highly correlated with the physiological and biochemical indicators under drought stress, especially the chlorophyll fluorescence parameters, such as the actual photosynthetic efficiency of photosystem II, electron transport rate, photochemical quenching coefficient, and the maximum quantum efficiency of photosystem II photochemistry. The majority of the response genes related to the metabolic pathways, including photosynthesis, sugar metabolism, and phytohormone signal pathway, were highly expressed under drought stress. In addition, genes associated with cell wall, pectin, and galacturonan metabolism also played crucial roles in the response of R. rex to drought stress. The results provided novel insight into the molecular response of the alpine woody species under drought stress and may improve the understanding of the response of forest ecosystems to the global climate change.

Characterization of the complete chloroplast genome sequence of wetland macrophyte Typha orientalis (Typhaceae).

Typha orientalis is an important wetland macrophyte native to the eastern parts of Asia and Oceania. Herein, the complete chloroplast genome of this species was assembled and characterized using whole-genome next-generation sequencing. The complete chloroplast genome showed a circular genome of 160,969 bp size with 36.6% GC content. The genome is of typical structure and contains a pair of inverted repeat (IR) regions with 26,691 bp, separated by one large single-copy (LSC) with 89,118 bp, and one small single-copy (SSC) regions with 18,469 bp. The genome contained 132 genes, including 86 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. A phylogenetic tree reconstructed based on 15 chloroplast genomes reveals that T. orientalis is most related to Typha latifolia.

Characterization of the complete chloroplast genome sequence of submerged macrophyte Stuckenia pectinata (Potamogetonaceae) and its phylogenetic position.

Stuckenia pectinata is widely distributed submerged macrophyte in the world. Herein, the complete chloroplast genome of this species was assembled and characterized using whole genome next-generation sequencing. The complete chloroplast genome showed a circular genome of 156,669 bp size with 36.5% GC content. The genome is of typical structure and contain a pair of inverted repeat (IR) regions with 26,074 bp, separated by one large single-copy (LSC) with 86,285 bp, and one small single-copy (SSC) regions with 18,236 bp. De novo assembly and annotation showed the presence of 131 unique genes with 85 protein-coding genes, 38 tRNA genes, and eight rRNA genes. A maximum-likelihood phylogenomic tree reconstructed based on 15 chloroplast genomes reveals that S. pectinata is most closely related to Zostera marina.