Abstract
Salt stress is one of the major devastating factors affecting the growth and yield of almost all crops, including the crucial staple food crop sweet potato. To understand their molecular responses to salt stress, comparative transcriptome and proteome analysis of salt-tolerant cultivar Xushu 22 and salt-sensitive cultivar Xushu 32 were investigated. The results showed the two genotypes had distinct differences at the transcription level and translation level even without salt stress, while inconsistent expression between the transcriptome and proteome data was observed. A total of 16,396 differentially expressed genes (DEGs) and 727 differentially expressed proteins (DEPs) were identified. Wherein, 1,764 DEGs and 93 DEPs were specifically expressed in the tolerant genotype. Furthermore, the results revealed that the significantly upregulated genes were mainly related to the regulation of ion accumulation, stress signaling, transcriptional regulation, redox reactions, plant hormone signal transduction, and secondary metabolite accumulation, which may be involved in the response of sweet potato to salt stress and/or may determine the salt tolerance difference between the two genotypes. In addition, 1,618 differentially expressed regulatory genes were identified, including bZIP, bHLH, ERF, MYB, NAC, and WRKY. Strikingly, transgenic Arabidopsis overexpressing IbNAC7 displayed enhanced salt tolerance compared to WT plants, and higher catalase (CAT) activity, chlorophyll and proline contents, and lower malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation were detected in transgenic plants compared with that of WT under salt stress. Furthermore, RNA-seq and qRT-PCR analysis displayed that the expression of many stress-related genes was upregulated in transgenic plants. Collectively, these findings provide revealing insights into sweet potato molecular response to salt stress and underlie the complex salt tolerance mechanisms between genotypes, and IbNAC7 was shown as a promising candidate gene to enhance salt tolerance of sweet potato.
Highlights
Plants are often permanently exposed to a variety of abiotic stresses, such as salinity, drought, heat, and cold
A total of 16,396 differentially expressed genes (DEGs) were identified from the fibrous root libraries under normal and salt-treated conditions based on the FDR < 0.05, and |log2| > 1 (Supplementary Figure S2, Supplementary Table S3)
4,460 and 6,150 DEGs were from Xu22-SR vs Xu22-CR and Xu32-SR vs Xu32-CR, respectively, 8,128 DEGs were from Xu22 vs Xu32 without salt stress, and 8,525 DEGs were from Xu22 vs Xu32 under salt stress
Summary
Plants are often permanently exposed to a variety of abiotic stresses, such as salinity, drought, heat, and cold. Significant progress has critically demonstrated that numerous NACs in various plant species are involved in diverse biological processes, especially in response to biotic and abiotic stress, such as drought, salt, and cold (Puranik et al, 2012; Mathew and Agarwal, 2018). Transgenic rice that overexpressed SNAC1 or SNAC2 genes displayed obviously improved tolerance to drought and salt, and the expression of lots of stress-related genes was upregulated in SNAC2overexpressing plants (Hu et al, 2006; Nakashima et al, 2007). Our previous study displayed that overexpression of a AP2/ERF gene, IbCBF3, increased the cold and drought tolerance in transgenic sweet potato (Jin et al, 2017). This study identified crucial genes/ proteins and pathways between the two contrasting cultivars under salt stress, and provided fundamental insights into the molecular mechanisms underlying sweet potato stress tolerance
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