Knock out of the PHOSPHATE 2 Gene TaPHO2-A1 Improves Phosphorus Uptake and Grain Yield under Low Phosphorus Conditions in Common Wheat

Abstract

MiR399 and its target PHOSPHATE2 (PHO2) play pivotal roles in phosphate signaling in plants. Loss of function mutation in PHO2 leads to excessive Pi accumulation in shoots and growth retardation in diploid plants like Arabidopsis thaliana and rice (Oryza sativa). Here we isolated three PHO2 homologous genes TaPHO2-A1, -B1 and -D1 from hexaploid wheat (Triticum aestivum). These TaPHO2 genes all contained miR399-binding sites and were able to be degraded by tae-miR399. TaPHO2-D1 was expressed much more abundantly than TaPHO2-A1 and -B1. The ion beam-induced deletion mutants were used to analyze the effects of TaPHO2s on phosphorus uptake and plant growth. The tapho2-a1, tapho2-b1 and tapho2-d1 mutants all had significant higher leaf Pi concentrations than did the wild type, with tapho2-d1 having the strongest effect, and tapho2-b1 the weakest. Two consecutive field experiments showed that knocking out TaPHO2-D1 reduced plant height and grain yield under both low and high phosphorus conditions. However, knocking out TaPHO2-A1 significantly increased phosphorus uptake and grain yield under low phosphorus conditions, with no adverse effect on grain yield under high phosphorus conditions. Our results indicated that TaPHO2s involved in phosphorus uptake and translocation, and molecular engineering TaPHO2 shows potential in improving wheat yield with less phosphorus fertilizer.

Phosphorus Transport in Arabidopsis and Wheat: Emerging Strategies to Improve P Pool in Seeds

“…This resembled the phenotype observed in a pho2 mutant of both monocots (e.g., rice) and dicots (e.g., Arabidopsis) [74,75]. Interestingly, tapho2-a1 knockout mutant plants showed reduced TaPHO2 expression that leads to only a moderate increase of total P and Pi levels in leaf under both sufficient and deficient P conditions [47]. Unlike the tapho2-d1 mutant, tapho2-a1 mutants demonstrated a moderate increase in P levels and accumulation alongside improved plant growth and grain yield [47].…”

“…It is still unclear whether transportation of P to the grain occurs directly from phloem or via xylem through recycling from roots, and to what extent translocation of P between plant organs is altered at different P-regimes [102]. In wheat, only two significant transgenic studies that include over-expression of TaPHR1-A1 and knockout of TaPHO2-A1 were able to achieve enhanced P uptake and grain yield under low Pi condition [47,49]. It is reasonable to speculate that manipulating these Pi-related genes, among others yet to be discovered, will allow intentional modulation of Pi loading in grains [20,88].…”

“…Unlike the tapho2-d1 mutant, tapho2-a1 mutants demonstrated a moderate increase in P levels and accumulation alongside improved plant growth and grain yield [47]. In light of these interesting data, the involvement of TaPHO2-D1 in Pi homeostasis to maintain plant growth rather than a simple Pi starvation signalling pathway has been proposed [47]. The Pi starvation signalling pathway PHR1-IPS1-miR399-UBC24/PHO2-PHT1/PHO1 seems to be conserved and functional in numerous plant species.…”

“…Interestingly, tapho2-a1 knockout mutant plants showed reduced TaPHO2 expression that leads to only a moderate increase of total P and Pi levels in leaf under both sufficient and deficient P conditions [47]. Unlike the tapho2-d1 mutant, tapho2-a1 mutants demonstrated a moderate increase in P levels and accumulation alongside improved plant growth and grain yield [47]. In light of these interesting data, the involvement of TaPHO2-D1 in Pi homeostasis to maintain plant growth rather than a simple Pi starvation signalling pathway has been proposed [47].…”

“…Detailed analysis of respective mutant lines for three TaPHO2 genes from homologous group1 (A1, B1, and D1) showed remarkably different effects on P uptake, distribution, and plant growth [47]. The overall expression of TaPHO2 in wheat was severely reduced in a tapho2-d1 mutant, leading to high total shoot P under limited Pi conditions, but also showed inhibited growth and yield [47]. This resembled the phenotype observed in a pho2 mutant of both monocots (e.g., rice) and dicots (e.g., Arabidopsis) [74,75].…”