Identification of Differentially Expressed Genes in Leaf of <i>Reaumuria soongorica</i> under PEG-Induced Drought Stress by Digital Gene Expression Profiling

<div><p><i>Reaumuria soongorica</i> (Pall.) Maxim., a resurrection semi-shrub, is a typical constructive and dominant species in desert ecosystems in northwestern China. However, the gene expression characteristics of <i>R. soongorica</i> under drought stress have not been elucidated. Digital gene expression analysis was performed using Illumina technique to investigate differentially expressed genes (DEGs) between control and PEG-treated samples of <i>R. soongorica</i>. A total of 212,338 and 211,052 distinct tags were detected in the control and PEG-treated libraries, respectively. A total of 1,325 genes were identified as DEGs, 379 (28.6%) of which were up-regulated and 946 (71.4%) were down-regulated in response to drought stress. Functional annotation analysis identified numerous drought-inducible genes with various functions in response to drought stress. A number of regulatory proteins, functional proteins, and proteins induced by other stress factors in <i>R. soongorica</i> were identified. Alteration in the regulatory proteins (transcription factors and protein kinase) may be involved in signal transduction. Functional proteins, including flavonoid biosynthetic proteins, late embryogenesis abundant (LEA) proteins, small heat shock proteins (sHSP), and aquaporin and proline transporter may play protective roles in response to drought stress. Flavonoids, LEA proteins and sHSP function as reactive oxygen species scavenger or molecular chaperone. Aquaporin and proline transporters regulate the distribution of water and proline throughout the whole plant. The tolerance ability of <i>R. soongorica</i> may be gained through effective signal transduction and enhanced protection of functional proteins to reestablish cellular homeostasis. DEGs obtained in this study may provide useful insights to help further understand the drought-tolerant mechanism of <i>R. soongorica</i>.</p></div

Selected DEGs between the C and P libraries.

<p>C represents the control group; P represents the PEG-treated group. The DEGs was selected through FDR ≤0.001 and |log₂Ratio| ≥1.</p

Categorization and abundance of tags.

<p>Clean tags are tags that remained after filtering out dirty tags (low quality tags) from raw data. Distinct tags are different kinds of tags. Unambiguous tags are clean tags remaining after the removal of tags mapped to reference sequences from multiple genes. C represents the control group; P represents the PEG-treated group.</p

Putative enzymes involved in digestion that were identified in <i>P</i>. <i>americana</i> midgut transcriptome.

<p>Putative enzymes involved in digestion that were identified in <i>P</i>. <i>americana</i> midgut transcriptome.</p

Distribution of total clean tag and distinct clean tag copy numbers from the libraries C and P.

<p>C represents the control group; P represents the PEG-treated group.</p

Gene ontology (GO) classification of the <i>P</i>. <i>americana</i> midgut transcriptome.

<p>Unigenes are classified into three main categories: biological process (A), cellular component (B) and molecular function (C).</p

Gene classification based on gene ontology (GO) for DEGs in C and P libraries of <i>R. soongorica</i>.

<p>Only the biological processes were used for GO analysis. C represents the control group; P represents the PEG-treated group.</p

Heteromorphic leaves of one <i>Populus euphratica</i> tree from bottom to top of the crown (Pe1–Pe12) at the <i>P</i>. <i>euphratica</i> Reserve in the Ejina Oasis.

<p>Pe1, linear leaf; Pe2, Pe3, lanceolate leaf; Pe4, ovate leaf; Pe5, Pe6, dentate ovate leaf; Pe7, Pe8, dentate rhombic leaf; Pe9, Pe10, dentate broad-ovate leaf; Pe11, Pe12, dentate fan-shaped leaf. From Pe5 to Pe12, the level of dentate degree increased.</p

Chloroplast ultrastructural characters in the mesophyll cells of <i>P</i>. <i>euphratica</i> heteromorphic leaves from Pe1 to Pe12.

<p>The images are shown in ×30,000 magnification, scale bars = 1 nm. Cp, chloroplast; Sg, starch grain.</p

Ranking of drought resistance in the development of <i>Populus euphratica</i> heteromorphic leaves based on subordinate function values.

<p>Mn, material number; Mv, mean value; Rn, Ranking number.</p><p>Ranking of drought resistance in the development of <i>Populus euphratica</i> heteromorphic leaves based on subordinate function values.</p