Abstract
Pomegranate (Punica granatum L.) is widely grown in arid and semi-arid soils, with constant soil salinization. To elucidate its molecular responses to salt stress on mRNA levels, we constructed 18 cDNA libraries of pomegranate roots and leaves from 0 (controls), 3, and 6 days after 200 mM NaCl treatment. In total, we obtained 34,047 genes by mapping to genome, and then identified 2255 DEGs (differentially expressed genes), including 1080 up-regulated and 1175 down-regulated genes. We found that the expression pattern of most DEGs were tissue-specific and time-specific. Among root DEGs, genes associated with cell wall organization and transmembrane transport were suppressed, and most of metabolism-related genes were over-represented. In leaves, 41.29% of DEGs were first suppressed and then recovered, including ions/metal ions binding-related genes. Also, ion transport and oxidation-reduction process were restricted. We found many DEGs involved in ABA, Ca2+-related and MAPK signal transduction pathways, such as ABA-receptors, Ca2+-sensors, MAPK cascades, TFs, and downstream functional genes coding for HSPs, LEAs, AQPs and PODs. Fifteen genes were selected to confirm the RNA-seq data using qRT-PCR. Our study not only illuminated pomegranate molecular responses to salinity, but also provided references for selecting salt-tolerant genes in pomegranate breeding processes.
Highlights
Soil salinization is defined as the excess or deposition of salt ions in land, which may interfere with plant growth
The ratios of reads mapping to the pomegranate genome were high, with values ranging from 93.61% to 95.33%
Under NaCl stress, we found that 12 of 19 NAC genes were up-regulated, and 10 of 19 genes were down-regulated in leaves or roots of pomegranate plants
Summary
Soil salinization is defined as the excess or deposition of salt ions in land, which may interfere with plant growth. Plants exposed to saline conditions mainly suffer from osmotic stress, ion toxicity, and nutrient deficiency [3,4]. All of the significant processes involved in plant growth and development, such as photosynthesis, protein synthesis, energy conversion and ion balance, could be affected by salinity [5]. Plants can adapt to saline environment with following strategies: (1) Efficiently controlling the uptake, transport, and compartmentalization of toxic ions; Agronomy 2020, 10, 44; doi:10.3390/agronomy10010044 www.mdpi.com/journal/agronomy (2) synthesis of osmoregulation substances and activation of antioxidant enzymes; (3) formation of unique morphological structures, such as succulent leaves, salt glands and bladders [7,8]
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