Abstract
BackgroundFoxtail millet (Setaria italica L. P. Beauv) has been considered as a tractable model crop in recent years due to its short growing cycle, lower amount of repetitive DNA, inbreeding nature, small diploid genome, and outstanding abiotic stress-tolerance characteristics. With modern agriculture facing various adversities, it’s urgent to dissect the mechanisms of how foxtail millet responds and adapts to drought and stress on the proteomic-level.ResultsIn this research, a total of 2474 differentially expressed proteins were identified by quantitative proteomic analysis after subjecting foxtail millet seedlings to drought conditions. 321 of these 2474 proteins exhibited significant expression changes, including 252 up-regulated proteins and 69 down-regulated proteins. The resulting proteins could then be divided into different categories, such as stress and defense responses, photosynthesis, carbon metabolism, ROS scavenging, protein synthesis, etc., according to Gene Ontology annotation. Proteins implicated in fatty acid and amino acid metabolism, polyamine biosynthesis, hormone metabolism, and cell wall modifications were also identified. These obtained differential proteins and their possible biological functions under drought stress all suggested that various physiological and metabolic processes might function cooperatively to configure a new dynamic homeostasis in organisms. The expression patterns of five drought-responsive proteins were further validated using western blot analysis. The qRT-PCR was also carried out to analyze the transcription levels of 21 differentially expressed proteins. The results showed large inconsistency in the variation between proteins and the corresponding mRNAs, which showed once again that post-transcriptional modification performs crucial roles in regulating gene expression.ConclusionThe results offered a valuable inventory of proteins that may be involved in drought response and adaption, and provided a regulatory network of different metabolic pathways under stress stimulation. This study will illuminate the stress tolerance mechanisms of foxtail millet, and shed some light on crop germplasm breeding and innovation.
Highlights
In the proteins with increased expression, 16 proteins showed increased levels of over 4 folds compared to that of the control, 87 showed increased levels between 2 and 4 folds than that of the control, and the remaining 149 proteins showed an Overview of quantitative proteomics analysis Referring to the classification criteria of the categories, these drought-responsive proteins could be further classified into different sub-categories
The subcellular localization analysis showed that these proteins were mainly localized in the chloroplast, cytoplasm, mitochondria, endoplasmic reticulum (ER), peroxisome, plasmodesma, extracellular space, nucleus, cytoskeleton, and vacuoles (Fig. 3a)
The functions of the proteins in these four clusters are generally focused on stress and defense response, photosynthesis, glycolysis, and protein synthesis; the abundance of most of these proteins increased, which displays the pivotal response of these proteins under drought conditions
Summary
P. Beauv) has been considered as a tractable model crop in recent years due to its short growing cycle, lower amount of repetitive DNA, inbreeding nature, small diploid genome, and outstanding abiotic stress-tolerance characteristics. Foxtail millet (Setaria italica L.) is an ancient crop in the subfamily of Panicoideae, and is distributed worldwide in arid and semi-arid regions. It originated in North China, and was domesticated more than 8,700 years ago. Foxtail millet carries attractive qualities such as a small diploid genome (~490 Mb), inbreeding nature, less repetitive DNA, short growing cycle and abiotic stress-tolerance [3].
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