Trait variations and expression profiling of OsPHT1 gene family at the early growth-stages under phosphorus-limited conditions

Abstract

To better understand the early response of genotypes to limited-phosphorus (P) conditions and the role of the phosphate transporter OsPHT1 gene family in the presence of PSTOL1, it is essential to characterize the level of tolerance in rice under limited-P conditions. In the present experiment, six rice genotypes were studied in three-way interactions [genotype (G) × phosphorus (P) × duration (D)] by comparing them at two instances (14 d and 28 d) under seven different concentrations of P (0.5‒10.0 ppm) in a hydroponic system. Trait differences and interactions of these traits were clearly distinguished among the various P rates. However, aboveground trait expression registered increased growth from 6.0 to 10.0 ppm of P. The major root-attributed traits in 0.5 ppm of P are significantly increased vis-à-vis 10 ppm of P. Analysis of variance displayed a significant difference between the genotypes for PSTOL1 and PHT1 expression. In low P, maximum root length with a shoot and root dry weight was observed in a new indigenous accession, IC459373, with higher expression of PSTOL1 than in Dular and IR64-Pup1 in 0.5 ppm of P at 14 d. Among the 13 PHT1 genes, OsPT1, OsPT2, OsPT6, and OsPT13 showed significant upregulation in IC459373, Dular, and IR64-Pup1. These results indicated that studying the expression levels of the PSTOL1 and PHT1 gene family at the early growth stages would be helpful in identifying superior donors to improve low-P tolerance and P-use efficiency in rice breeding programs.

Figure 1

Concentration-by-trait biplot based on the variance exhibited by selected traits under different concentrations of phosphorus explained by two principal component axes: (a) 14 days after sowing and (b) 28 days after sowing.

Figure 2

Percentage contribution of shoot/leaf/root to the whole plant under different concentrations of phosphorus in a hydroponic experiment at 14 d and 28 d. Vertical bars represent standard deviation. *p = 0.05 at 14 d, †p = 0.05 at 28 d.

Figure 3

Phenotypic relationship between root dry weight and root parameters across different concentrations of phosphorus under hydroponics at 14 (red = ◊) and 28 (blue = □) days after sowing. ⊠ − 0.5 ppm, ♦ − 1 ppm, ▲ − 2 ppm, ● − 4 ppm,  − 6 ppm, ■ − 8 ppm, and  − 10 ppm.

Figure 4

The correlation coefficient between morphological and physiological traits at 14 d and 28 d. a = correlation coefficient at 14 d in 0.5 ppm of P, b = correlation coefficient at 14 d in 10.0 ppm of P, c = correlation coefficient at 28 d in 0.5 ppm of P, and d = correlation coefficient at 28 d in 10.0 ppm of P. DL: number of dry leaves; L_V: root length per volume; LA: leaf area (cm²); LDW: leaf dry weight (g); LL: leaf length (cm); LNo: number of leaves; LW: leaf width (cm); PH: shoot length (cm); PL: number of pigmented leaves; PRA: projected root area (cm²); R.S: root-to-shoot ratio; R_P: root P content (mg/g); R_V: root volume (cm³); RAD: average root diameter (mm); RDW: root dry weight (g); RL: max. root length (cm); RSA: root surface area (cm²); S_d: stem diameter (mm); S_P: shoot P content (mg/g); SDW: shoot dry weight (g); SPAD; TRL: total root length (cm).

Figure 5

Genotype-by-trait biplot based on the variance exhibited by selected traits under different concentrations of phosphorus explained by two principal component axes: (a) 14 days after sowing and (b) 28 days after sowing.

Figure 6

Percentage contribution of shoot/leaf/root dry weight in the total plant weight of genotypes across a different concentration of phosphorus in the hydroponic experiment at 14 d and 28 d. Vertical bars represent standard deviation. *p = 0.05 at 14 d, †p = 0.05 at 28 d.

Figure 7

Expression analysis of PSTOL1 and OsPT genes in rice in different concentrations of P. (a) Relative fold change in expression of OsPT genes between the genotypes in 0.5 ppm of P concentration, (b) relative fold change in expression of OsPT genes between the genotypes in 4.0 ppm of P concentration, (c) relative fold change in expression of OsPT genes between the genotypes in 10.0 ppm of P concentration, (d) relative fold change in expression of OsPT genes from 0.5 ppm to 4.0 ppm of P concentration, (e) relative fold change in expression of OsPT genes between 10.0 ppm and 4.0 ppm of P concentration, and (f) fold change in expression of PSTOL1 between 0.5 ppm and 4.0 ppm and 100 ppm and 4.0 ppm of P concentration.

Figure 8

Average number of crown roots across genotypes under different concentrations of phosphorus in the hydroponic experiment at 14 d and 28 d. The vertical bar represents the standard deviation.

Figure 9

Heat map showing the grouping of genotypes based on similarity in expression of root and shoot vigor under different concentrations of P at 14 d. S_lth: shoot length (cm); SPAD; R_Surf_Area: root surface area (cm²); P_R_Area: projected root area (cm²); RL: max. root length (cm); LL: leaf length (cm); T_R_lth: total root length (cm); R_Len_Vol: root length per volume.

Figure 10

A schematic view of phenotypic screening under different concentrations of phosphorus and expression profiling of rice genotypes. Schematic representation of genotypes with the shoot and root vigor at 14 days (3‒4-leaf stage) after sowing in response to low P under direct-seeded (a) and nursery (b) conditions. (a) Low-phosphorus soil—young seedling under direct-seeded conditions: 1 = poor root and shoot vigor, 2 = root vigor but poor shoot growth, 3 = high root and shoot vigor. (b) Low-phosphorus soil—young seedling in the nursery: 1 = poor root and shoot vigor, 2 = poor root vigor but good shoot growth, 3 = high root and shoot vigor.