Identifying biomarkers for low phosphorus tolerance in soybean

Soybean (Glycine max) is an important food crop worldwide and has been grown in China for over 5000 years. Soybeans are a remarkably nutritious, its seeds are enriched with high levels of proteins (40–50 %), fats (20–30 %) and vital phytochemicals, including anthocyanins, tocopherols, isoflavones and saponins. Soybean plants also have key agroecological benefits in cropping systems, such as soil carbon sequestration and nitrogen fixation. However, soybean yield is strongly affected by soil phosphorus (P) availability. Although studies have been carried out to investigate the molecular responses of soybean to the shortage of P in soil, these focussed on the transcriptome and metabolome. Proteins represent the actual functional molecules in the cell and are highly affected by abiotic stresses. Comparing the proteome of soybean genotypes with contrasting low-P tolerance levels will allow us to pinpoint major proteins and pathways involved in P-deficiency tolerance.

In their recent study published in AoBP, Zhao et al. conducted a comparative proteomics study of two soybean genotypes with contrasting responses to low-P. They explored the proteome differences in roots of low-P-tolerant and low-P-sensitive soybean genotypes under different concentrations of P using the Tandem Mass Tag (TMT)-based comparative proteomics approach. Understanding such responses may help plant breeders to develop soybean varieties that are more tolerant to low-P conditions.

A total of 41,678 peptides, 19,612 unique peptides and 4126 proteins were identified in the study. Increased numbers of differentially expressed proteins (DEPs) were obtained from low-P and P-free conditions compared to the normal-P treatment. All 660 DEPs obtained in the low-P tolerant genotype were upregulated in response to P deficiency, while most DEPs detected in the low-P sensitive genotype were downregulated under P deficiency. Identifying potential biomarkers for low-P tolerance will be useful for rapid screening across populations. In this study, three proteins (I1KW20 (prohibitins), I1K3U8 (alpha-amylase inhibitors) and C6SZ93 (alpha-amylase inhibitors)) in particular were found to be constantly upregulated in the tolerant genotype but not affected in the sensitive line, making them ideal candidates as biomarkers for low-P tolerance.

In their work, Zhao et al. observed that important metabolic pathways, such as oxidative phosphorylation, glutathione metabolism and carbon metabolism, were suppressed in the sensitive genotype. In contrast, the tolerant genotype increased the metabolic activity in certain pathways, such as 2-oxocarboxylic acid metabolism, carbon metabolism, glycolysis and biosynthesis of amino acids, in order to maintain normal growth under P deficiency. The authors suggest that an interesting follow-up experiment may be to test mutant plants of the sensitive genotype over-expressing the three putative key adaptive proteins in P-limited conditions, to assess whether they indeed confer tolerance to low-P conditions.