Transcriptomic Analysis Reveals the Mechanism of Picea crassifolia Survival for Alpine Treeline Condition

Abstract

The physiological mechanisms driving treeline formation succession captured the attention of ecologists many years ago, yet they are still not fully understood. In this study, physiological parameters (soluble sugars, starch, and nitrogen) were investigated in combination with transcriptomic analysis in the treeline tree species Picea crassifolia. The study was conducted in the middle of Qilian Mountain Reserves, Gansu Province, China, within the elevation range of 2500–3300 m. The results showed that the concentrations of non-structural carbohydrates decreased with increasing elevation in the current-year needles and current-year branches, as well as in the coarse and fine roots. RNA-Seq demonstrated that 483 genes were upregulated and 681 were downregulated in the comparison of 2900 and 2500 m (2900 vs. 2500), 770 were upregulated and 1006 were downregulated in 3300 vs. 2500, and 282 were upregulated and 295 were downregulated in 3300 vs. 2900. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the differentially expressed genes were highly enriched in photosynthesis-related processes, carbon fixation and metabolism, and nitrogen metabolism. Furthermore, almost all photosynthesis-related genes were downregulated, whereas many genes involved in cuticle lipids and flavonoid biosynthesis were upregulated, contributing to the survival of P. crassifolia under the treeline condition. Thus, our study provided not only molecular evidence for carbon limitation hypothesis in treeline formation, but also a better understanding of the molecular mechanisms of treeline tree survival under adverse conditions.

Acclimation Strategy of Masson Pine (Pinus massoniana) by Limiting Flavonoid and Terpenoid Production under Low Light and Drought

“…Total RNAs were isolated from 3 kinds of tissues (leaves, phloem, and xylem from the current-year branches) using a Sangon Total RNA Purification Kit according the manufacturer’s protocol (Shanghai Sangon, Shanghai, China). The libraries were constructed and sequenced with the Illumina HiSeq 2500 platform (Illumina, San Diego, CA, USA), as described in our previous report [ 25 ]. An index of the reference genome was built using Bowtie v2.0.6, and single-end clean reads were aligned with the reference genome using TopHat v2.0.9 [ 49 ].…”

“…A study of two-year drought stress on eleven tree species (six gymnosperm and five angiosperm species) demonstrated that the drought-resistant species had higher contents of flavonoids and polyphenols accompanied by higher leaf mass per area and higher photosynthetic rate [ 24 ]. In addition, many genes involved in flavonoid biosynthesis were found to be upregulated, while most photosynthesis-related genes were downregulated, in Picea crassifolia at a higher elevation compared to a lower one [ 25 ]. These results have demonstrated that polyphenols may play key roles in the survival of trees under various stress conditions.…”

Elevation Effects on Growth Pattern and Resource Allocation of <i>Picea crassifolia</i> in Qilian Mountains, Northwest China

“…and also explored the causes of growth cessation in Qinghai spruce under the climate change [31]. However, no combined BAI was available to study the factors limiting the growth of Qinghai spruce at different elevations [32,33]. In this paper, we have calculated the BAI of Qinghai spruce using the original tree ring width chronology method and compared the patterns of change in NSC and its components' concentrations between the elevations and tissues available in the Qilian Mountains.…”