Fig. 3: Mild drought induces PSR in field-grown soybean plants.

a Positions of the second trifoliate leaves (dotted enclosure) used for RNA-seq analysis in 29-day-old soybean plants grown on flats and ridges in 2015. Bars, 10 cm. b Schematic representation of a soybean plant. c Heatmap of log₂ fold-change in expression of 990 up-regulated and 400 down-regulated genes (|log₂(FC)| ≥ 1, FPKM value > 0, q < 0.05) under mild drought conditions induced by ridges. PSR genes are indicated on the lower row. F and R denote flats and ridges, respectively. d Ratio of PSR marker genes to the total number of genes, the number of up-regulated genes, and the number of down-regulated genes. e Representative up-regulated PSR marker genes under mild drought conditions. f PSR gene expression determined using RT-qPCR in the first to third trifoliate leaves of 29-day-old plants grown on ridges and flats in 2015 (n = 9 biologically independent replicates for the second trifoliate leaves; n = 10 biologically independent replicates for the first and third trifoliate leaves). The actin gene (Glyma.15G050200) was used as an internal control for gene expression. g Pi concentration of first to third trifoliate leaves of soybean plants grown on ridges and flats; same samples described in f. ^*P < 0.05, ^**P < 0.01, and ^***P < 0.001, one-way analysis of variance (ANOVA) with Tukey’s test in ridged versus flat plots for each leaf position; ns, no significant difference. Error bars denote SD.