Transcriptome and structure analysis in root of Casuarina equisetifolia under NaCl treatment

Abstract

Background High soil salinity seriously affects plant growth and development. Excessive salt ions mainly cause damage by inducing osmotic stress, ion toxicity, and oxidation stress. Casuarina equisetifolia is a highly salt-tolerant plant, commonly grown as wind belts in coastal areas with sandy soils. However, little is known about its physiology and the molecular mechanism of its response to salt stress. Results Eight-week-old C. equisetifolia seedlings grown from rooted cuttings were exposed to salt stress for varying durations (0, 1, 6, 24, and 168 h under 200 mM NaCl) and their ion contents, cellular structure, and transcriptomes were analyzed. Potassium concentration decreased slowly between 1 h and 24 h after initiation of salt treatment, while the content of potassium was significantly lower after 168 h of salt treatment. Root epidermal cells were shed and a more compact layer of cells formed as the treatment duration increased. Salt stress led to deformation of cells and damage to mitochondria in the epidermis and endodermis, whereas stele cells suffered less damage. Transcriptome analysis identified 10,378 differentially expressed genes (DEGs), with more genes showing differential expression after 24 h and 168 h of exposure than after shorter durations of exposure to salinity. Signal transduction and ion transport genes such as HKT and CHX were enriched among DEGs in the early stages (1 h or 6 h) of salt stress, while expression of genes involved in programmed cell death was significantly upregulated at 168 h, corresponding to changes in ion contents and cell structure of roots. Oxidative stress and detoxification genes were also expressed differentially and were enriched among DEGs at different stages. Conclusions These results not only elucidate the mechanism and the molecular pathway governing salt tolerance, but also serve as a basis for identifying gene function related to salt stress in C. equisetifolia.

Salt Stress Tolerance in Casuarina glauca: Insights from the Branchlets Transcriptome

“…The results are rather different from those reported for the C. glauca branchlets’ proteome [ 30 ], and metabolome [ 25 , 26 , 27 ], where changes were associated to major physiological changes related to photosynthesis, membrane stability and osmoprotection mechanisms [ 22 , 24 , 25 , 26 , 27 ]. This reinforces the hypothesis that C. glauca has a strong stress-responsive system with an extensive set of constitutive defense mechanisms [ 7 , 43 ] complemented by rapid induction of transcriptional changes at the initial stages of salt exposure [ 37 , 40 ]. Despite the differences associated with the molecular changes imposed during the nodulation process (highlighted above), in both plant groups the top-ten up-regulated DEGs were related to signaling, transport, refolding, and stomatal control ( Table 1 , Table 2 , Table 3 , Table 4 and Table 5 ; Figures S4 and S5 ).…”

“…75–95 million clean reads comprising ca. 53,000–72,000 unigenes [ 37 ]. Finally, Wang et al [ 40 ] reported ca.…”

“…Nevertheless, in this case, the fraction of positively regulated genes was higher than that of the negatively regulated ones. On the other hand, the number of DEGs reported in C. equisetifolia seedlings was considerably higher: >6000 DEGs in roots from plants exposed to 200 mM NaCl for seven days [ 37 ] and >4000 DEGs in leaves of plants exposed to cold [ 38 ]. However, in both cases the fold-change, rather than the statistical significance, has been privileged.…”

“…These included auxin- (400 KNO 3 + ) and abscisic acid (ABA)-activated signaling (600 KNO 3 + ; 600 NOD + ); Myb transcription factors and jasmonic acid signaling (400 NOD + ), regulation of sulphur utilization, transporter activity, and protein refolding (400- and 600- KNO 3 + ; 400- and 600 NOD + ), and response to cellular CO2/regulation of stomatal opening (600 KNO 3 + ; 600 NOD + ). It is widely known that the mechanisms used by plants to cope with salt stress are highly dependent on a coordinated set of events that regulates growth, metabolism, and homeostasis [ 37 , 44 , 45 ]. In halophytic plants, gene regulatory networks are an essential part of salt tolerance.…”

“…Recent transcriptomic studies provided relevant information about the mechanisms underlying the ability of halophyte plants to endure high salt concentrations. Although gene interactions are complex and vary according to plant organ, age, and species, key genes related to salt-tolerance are often related to hormone signaling pathways that regulate cell homeostasis and prevent oxidative damage [ 35 , 36 , 37 ].…”