A PSTOL-like gene, TaPSTOL, controls a number of agronomically important traits in wheat

Abstract

Background: Phosphorus (P) is an essential macronutrient for plant growth, and is required in large quantities by elite varieties of crops to maintain yields. Approximately 70% of global cultivated land suffers from P deficiency, and it has recently been estimated that worldwide P resources will be exhausted by the end of this century, increasing the demand for crops more efficient in their P usage. A greater understanding of how plants are able to maintain yield with lower P inputs is, therefore, highly desirable to both breeders and farmers. Here, we clone the wheat (Triticum aestivum L.) homologue of the rice PSTOL gene (OsPSTOL), and characterize its role in phosphate nutrition plus other agronomically important traits.

Results: TaPSTOL is a single copy gene located on the short arm of chromosome 5A, encoding a putative kinase protein, and shares a high level of sequence similarity to OsPSTOL. We re-sequenced TaPSTOL from 24 different wheat accessions and (3) three T. durum varieties. No sequence differences were detected in 26 of the accessions, whereas two indels were identified in the promoter region of one of the durum wheats. We characterised the expression of TaPSTOL under different P concentrations and demonstrated that the promoter was induced in root tips and hairs under P limiting conditions. Overexpression and RNAi silencing of TaPSTOL in transgenic wheat lines showed that there was a significant effect upon root biomass, flowering time independent of P treatment, tiller number and seed yield, correlating with the expression of TaPSTOL. However this did not increase PUE as elevated P concentration in the grain did not correspond to increased yields.

Conclusions: Manipulation of TaPSTOL expression in wheat shows it is responsible for many of the previously described phenotypic advantages as OsPSTOL except yield. Furthermore, we show TaPSTOL contributes to additional agronomically important traits including flowering time and grain size. Analysis of TaPSTOL sequences from a broad selection of wheat varieties, encompassing 91% of the genetic diversity in UK bread wheat, showed that there is very little genetic variation in this gene, which would suggest that this locus may have been under high selection pressure.

Keywords: Flowering time; P; PSTOL; PUE; Phosphate; Seed number; Seed size; Wheat.

Fig. 1

Expression of TaPSTOL mRNA in wheat grown under a range of P concentrations. Expression of TaPSTOL in (a) roots and (b) shoots is shown relative to TaUbiquitin mRNA after seven days growth in hydroponic solution. Error bars are SE of three biological replications. Letters represent a significant difference (p val < 0.05) between the same tissue type at any P concentration

Fig. 2

Characterisation of TaPSTOL promoter-GUS transcriptional fusions in wheat. Seedlings were grown in sand watered with –P hydroponic solution for 10 days after germination. Low magnification of a multiple coleoptiles, b a single coleoptile, c leaf trichomes. d Higher magnification of trichomes. Low magnification of (e) multiple roots, (f) isolated roots. Higher magnification of lateral root initials (g, h). Low magnification of root system (i), shoots (j), four plants showing TaPSTOL:GUS expression (k), non-transformed control plant (l) grown under same conditions

Fig. 3

Agronomic measurements of OE and RNAi lines. Plants were grown under both low P (3 μM) conditions in sand to seed (a-d) or grown in M2 compost to seed (e-g). Dry weight of transgenic wheat a roots, or b shoots; c average tiller number; d yield per plant; e dry weight of shoots; faverage tiller number; g yield per plant. Asterisk indicates significant difference p val < 0.05 to WT Fielder

Fig. 4

Flowering time measurements of OE and RNAi lines. Days to flowering, defined as Zadok stage 49, is shown under either a low phosphate conditions in sand (3 μM P) or b M2 compost conditions. Asterisk indicates significant difference p val < 0.05 to WT Fielder

Fig. 5

Seed yield parameters of OE and RNAi lines. Number of seeds per plant and thousand grain weight for TaPSTOL modified transgenic wheat plants when grown in a and b sand with low P conditions (3 μM); or c and d in M2 compost. Asterisk indicates significant difference, p val < 0.05 relative to WT Fielder

Fig. 6

Comparison of seed size from TaPSTOL RNAi or OE plants. Ten seeds of TaPSTOL RNAi or OE lines plus WT Fielder grown on low P (3 μM P) on sand

Fig. 7

P concentration in roots, shoots and grains from TaPSTOL OE and RNAi plants. a Roots or shoots grown on low P in sand (3 μM); b Roots or shoots grown on M2 compost. c Grains harvested from TaPSTOL transgenic wheat plants grown on either low P or compost. Asterisk indicates significant difference, p val < 0.05 relative to WT Fielder

Fig. 8

PPUE and PER of transgenic wheat plants. Plants were grown under both low P (3 μM) conditions in sand to seed (a and b) or grown in M2 compost to seed (c and d). Double asterisk indicates significant difference p val < 0.01 to WT Fielder