Abstract
Main conclusion
SbCASP4 improves the salt tolerance of sweet sorghum [Sorghum bicolor (L.) Mocnch] by enhancing the root apoplastic barrier and blocking the transport of sodium ions to the shoot.
Abstract
Sweet sorghum [Sorghum bicolor (L.) Mocnch] is a C4 crop with high biomass and tolerance to abiotic stresses such as salt, drought, and waterlogging. Sweet sorghum is widely used in bioenergy production, as a forage crop, and in liquors and beer. Root salt exclusion has been reported to underlie the salt tolerance of sweet sorghum. The Casparian strip has a key role in root salt exclusion, and the membrane domain protein (CASP) family participates in Casparian strip aggregation. However, the function and the regulatory mechanisms of SbCASP in response to salt stress in sweet sorghum are unclear. In the current study, we cloned SbCASP4 and determined that it is induced by salt stress and expressed in the endodermis cells of sweet sorghum. Histochemical staining and physiological indicators showed that heterologous expression of SbCASP4 significantly increased the tolerance to salt stress in transgenic Arabidopsis thaliana. Compared with wild type and casp5 mutants, under 50 mM NaCl treatment, SbCASP4-expression lines had the less leaf Na+, lower PI accumulation in stele, smaller oxidative damage and higher salinity threshold, longer root length and higher expression levels of the genes related to Casparian strip formation.
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Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
This work was supported by the NSFC (National Natural Science Research Foundation of China; project nos. 31770288 and 31600200), the Shandong Province Key Research and Development Plan (2017CXGC0313), and the Natural Science Research Foundation of Shandong Province (ZR2014CZ002; ZR2017MC003).
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Supplementary file1 Figure S1. The map of vectors: pCAMBIA 1300 (a); pCAMBIA 3301 (b). (JPG 1341 KB)
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Supplementary file2 Figure S2. Temporal expression pattern of SbCASP4 in sweet sorghum roots (M-81E) at stage I and II under150 mM NaCl. (JPG 2000 KB)
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Supplementary file3 Figure S3. Phylogenetic tree of sorghum and Arabidopsis CASP genes (a), and phylogenetic tree of sorghum and rice CASP genes (b). (JPG 4173 KB)
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Supplementary file4 Figure S4. Identification of positive Arabidopsis transgenic lines. a: PCR identification of 35S:SbCASP4-GFP-positive lines. b: The relative expression levels of SbCASP4 in different lines. Values are means ± SD (n = 3). Different letters indicate significant differences at P = 0.05 as determined by Duncan′s multiple range test. c: PCR identification of pSbCASP4:SbCASP4-GFP-positive lines. d: PCR identification of pSbCASP4:GUS-positive lines. (JPG 2795 KB)
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Supplementary file5 Figure S5. Screening of the Arabidopsis homozygous casp5 mutants, (CS1015546) the Arabidopsis homolog of SbCASP4, and identification of T-DNA insertion sites. a: PCR identification of CS1015546 in the casp5 mutants, M: 2,000 bp DNA Marker; b: Sequencing identification of primer RP + pSKTAIL-L1; The red arrow indicates the insertion position of the T-DNA; c: Diagram of the T-DNA insertion site. (JPG 4203 KB)
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Supplementary file6 Figure S6. K+ content of shoot (a) and root (b) of the Arabidopsis wild-type, casp5 mutant, and SbCASP4-expression lines under 0 and 50 mM NaCl for 5 days. Values are means ± SD (n = 3). Different letters indicate significant differences at P = 0.05 as determined by Duncan′s multiple range test. (JPG 2915 KB)
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Supplementary file7 Figure S7. The relative expression levels of ion transporter genes in the Arabidopsis wild-type, casp5 mutant, and SbCASP4-expression lines under 0 and 50 mM NaCl for 5 days. SbCASP4 does not affect the expression of ion transporter genes. (a) AtSOS1; (b) AtHKT1; (c) AtNHX1. Values are means ± SD (n = 3). Different letters indicate significant differences at P = 0.05 as determined by Duncan’s multiple range test. (JPG 2400 KB)
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Wei, X., Liu, L., Lu, C. et al. SbCASP4 improves salt exclusion by enhancing the root apoplastic barrier. Planta 254, 81 (2021). https://doi.org/10.1007/s00425-021-03731-z
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DOI: https://doi.org/10.1007/s00425-021-03731-z