Proteome profiling reveals changes in energy metabolism, transport and antioxidation during drought stress in Nostoc flagelliforme

Abstract

Background: Drought is an important abiotic stress that constrains the growth of many species. Despite extensive study in model organisms, the underlying mechanisms of drought tolerance in Nostoc flagelliforme remain elusive.

Results: We characterized the drought adaptation of N. flagelliforme by a combination of proteomics and qRT-PCR. A total of 351 differentially expressed proteins involved in drought stress adaptation were identified. It was found that the expression of several nutrient influx transporters was increased, including molybdate ABC transporter substrate binding protein (modA), sulfate ABC transporter substrate-binding protein (sbp) and nitrate ABC transporter (ntrB), while that of efflux transporters for toxic substances was also increased, including arsenic transporting ATPase (ArsA), potassium transporter (TrkA) and iron ABC transporter substrate-binding protein (VacB). Additionally, photosynthetic components were reduced while sugars built up during drought stress. Non-enzymatic antioxidants, orange carotenoid protein (OCP) homologs, cytochrome P450 (CYP450), proline (Pro) and ascorbic acid (AsA) were all altered during drought stress and may play important roles in scavenging reactive oxygen species (ROS).

Conclusion: In this study, N. flagelliforme may regulates its adaptation to drought stress through the changes of protein expression in photosynthesis, energy metabolism, transport, protein synthesis and degradation and antioxidation.

Highlights: • A total of 351 DEPs involved in adaptation to drought stress were identified. • Changes in the expression of six OCP homologs were found in response to drought stress. • Differential expression of transporters played an important role in drought stress adaptation. • Most PSII proteins were downregulated, while PSI proteins were unchanged in response to drought stress. • Sugar metabolism was upregulated in response to drought stress.

Keywords: Differential expression; Drought stress; Functional analysis; Nostoc flagelliforme; Proteome.

Fig. 1

Profiling and validation of the proteome results of N. flagelliforme. A General overview of the steps involved; B Quantitative statistics for differentially expressed proteins (DEPs); C. PRM analysis of GST, Prx and PRK under drought stress in N. flagelliforme. The values are represented as means ± SD (n = 3) in the study (P < 0.05)

Fig. 2

GO and KEGG pathway analyses of differentially expressed proteins in N. flagelliforme under drought stress. A GO analysis; B KEGG pathway analysis

Fig. 3

Protein expression trends of N. flagelliforme under drought stress. A All expression trends; B Trends of differential protein expression of N. flagelliforme under drought stress. Significant trends were found in Cluster 2, Cluster 15, Cluster 13 and Cluster 14

Fig. 4

The protein interaction network of N. flagelliforme under drought stress. Npun_F5517 is PsbP, Npun_F4810 is PsbO, Npun_R2847 is M16, Npun_F4960 is TrkA, Npun_F3527 is GST, Npun_F2147 is ArsA, htpX is M48, Npun_F6222 is VacB, Npun_F3917 is FBP, Npun_F5056 is S41 and Npun_F3917 is GlpX

Fig. 5

Changes in the metabolite contents and key enzyme activities of N. flagelliforme under drought stress. Different letters on each bar indicate significantly different values (P < 0.05). The values are presented as means ± standard deviation (n = 3) (P < 0.05)

Fig. 6

Gene expression under different drought stress conditions. Values (means ± SD) were determined with three replicates. The values are presented as means ± SD (n = 3) (P < 0.05)

Fig. 7

Expression of orange carotenoid proteins (OCPs) in N. flagelliforme under drought stress. A. Comparison of the abundance of OCPs; B. Visualization of OCPs. The proteins that increased and decreased in abundance are indicated in yellow and blue, respectively

Fig. 8

Protein molecular regulation network in N. flagelliforme under drought stress. Proteins (drought stress vs. control) that were upregulated are colored red, while proteins (drought stress vs. control) that were downregulated are colored blue