Polyphosphate Accelerates Transformation of Nonstructural Carbohydrates to Improve Growth of ppk-Expressing Transgenic Rice in Phosphorus Deficiency Culture

doi:10.1016/j.rsci.2023.03.007

Abstract

Abstract:

Crop yield and quality are often limited by the amount of phosphate fertilizer added to infertile soils, a key limiting factor for sustainable development in modern agriculture. The polyphosphate kinase (ppk) gene -expressing transgenic rice with a single-copy line (ETRS) is constructed to improve phosphate fertilizer utilization efficiency for phosphorus resource conservation. To investigate the potential mechanisms of the increased biomass in ETRS in low phosphate culture, ETRS was cultivated in a low inorganic phosphate (Pi) culture medium (15 μmol/L Pi, LP) and a normal Pi culture medium (300 μmol/L Pi, CP), respectively. After 89 d of cultivation in different concentrations of phosphate culture media, the total phosphorus, polyphosphate (polyP), biomass, photosynthetic rate, nonstructural carbohydrate (NSC) contents, related enzyme activities, and related gene expression levels were analyzed. The results showed that ETRS had a high polyP amount to promote the photosynthetic rate in LP, and its biomass was almost the same as the wild type (WT) in CP. The NSC content of ETRS in LP was higher than that of WT in LP, but slightly lower than that of WT in CP. PolyP notably promoted the sucrose phosphate synthase activities of ETRS and significantly down-regulated the expression levels of sucrose transporter genes (OsSUT3 and OsSUT4), resulting in inhibiting the transport of sucrose from shoot to root in ETRS. It was concluded that polyP can stimulate the synthesis of NSCs in LP, which improved the growth of ETRS and triggered the biological activities of ETRS to save phosphate fertilizer. Our study provides a new way to improve the utilization rate of phosphate fertilizer in rice production.

Key words: polyphosphate, phosphate fertilizer, nonstructural carbohydrate, sucrose transporter gene, sucrose phosphate synthase

Zhu Jinling, Wei Ruping, Wang Xin, Zheng Chaoqun, Wang Mengmeng, Yang Yicheng, Yang Liuyan. Polyphosphate Accelerates Transformation of Nonstructural Carbohydrates to Improve Growth of ppk-Expressing Transgenic Rice in Phosphorus Deficiency Culture[J]. Rice Science, 2023, 30(3): 235-246.

Figures/Tables 7

Fig. 1. Phenotypes and biomasses in ETRS and wild type (WT) in different phosphate concentration culture media. A, Morphologies of ETRS and WT in LP and CP culture media. Scale bar is 10 cm.B?D, Total (B), root (C) and shoot (D) biomasses of ETRS and WT. Data represent Mean ± SD (n = 3). Different lowercase letters above the bars indicate significant differences between ETRS and WT (P < 0.05).ETRS, Polyphosphate kinase (ppk) gene-expressing transgenic rice with a single-copy line; LP, Low inorganic phosphate (Pi) culture medium (15 μmol/L); CP, Normal Pi culture medium (300 μmol/L).

Fig. 2. Relative expression level of ppk gene, and total phosphorus (P) and polyphosphate (polyP) contents in ETRS in different phosphate concentration culture media. A, Relative expression level of polyphosphate kinase (ppk) gene in response to LP and CP. RNA was extracted from rice roots and shoots at the full heading stage. Actin was used as an internal reference. B, Total P contents of ETRS and WT. C, Total P contents in roots of ETRS and WT. D, Total P contents in shoots of ETRS and WT. E, PolyP contents of ETRS and WT. ETRS, ppk gene-expressing transgenic rice with a single-copy line; WT, Wild type; LP, Low inorganic phosphate (Pi) culture medium (15 μmol/L); CP, Normal Pi culture medium (300 μmol/L); ND, Not detected.Data represent Mean ± SD (n = 3). Different lowercase letters above the bars indicate significant differences between ETRS and WT (P < 0.05).

Table 1. Contents of carbohydrate componants in ETRS and WT in different phosphate concentration culture media. mg/g

Treatment	Rice	Sucrose content		Total soluble sugar content		Starch content		NSC content
Treatment	Rice	Root	Shoot	Root	Shoot	Root	Shoot	Root	Shoot
LP	ETRS	19.4 ± 2.2 a	31.6 ± 4.3 a	24.5 ± 1.1 b	47.6 ± 4.0 a	191 ± 18 a	121 ± 18 a	215.5 ± 19.1 a	168.6 ± 22.0 a
LP	WT	22.0 ± 1.1 a	28.6 ± 3.3 a	29.3 ± 2.0 a	45.3 ± 3.6 a	179 ± 13 a	99 ± 8 b	208.3 ± 15.0 a	144.3 ± 11.6 b
CP	ETRS	21.6 ± 2.6 a	38.2 ± 5.3 a	25.3 ± 2.9 a	69.8 ± 3.0 a	208 ± 38 a	153 ± 8 a	233.3 ± 40.9 a	222.8 ± 11.0 a
CP	WT	19.3 ± 3.3 a	35.8 ± 1.9 a	28.9 ± 1.6 a	61.9 ± 6.5 a	213 ± 23 a	149 ± 13 a	241.9 ± 24.6 a	210.9 ± 19.5 a

Fig. 3. Photosynthesis related attributes in shoot of ETRS and WT in different phosphate concentration culture media. A, Photosynthetic rate of ETRS and WT shoots in different phosphate concentration culture media. B, Stomatal conductance of ETRS and WT shoots in different phosphate concentration culture media.. C, Intercellular CO2 concentration of ETRS and WT shoots in different phosphate concentration culture media.. ETRS, Polyphosphate kinase (ppk) gene-expressing transgenic rice with a single-copy line; WT, Wild type; LP, Low inorganic phosphate (Pi) culture medium (15 μmol/L); CP, Normal Pi culture medium (300 μmol/L). Data represent Mean ± SD (n = 3). Different lowercase letters above the bars indicate significant differences between ETRS and WT (P < 0.05).

Fig. 4. Sucrose synthase (SS, A) and sucrose phosphate synthase (SPS, B) activities in shoots of ETRS and WT in different phosphate concentration culture media. ETRS, Polyphosphate kinase (ppk) gene-expressing transgenic rice with a single-copy line; WT, Wild type; LP, Low inorganic phosphate (Pi) culture medium (15 μmol/L); CP, Normal Pi culture medium (300 μmol/L). Data represent Mean ± SD (n = 3). Different lowercase letters above the bars indicate significant differences between ETRS and WT (P < 0.05).

Fig. 5. Relative expression levels of OsSUT genes in shoots of ETRS and WT in different phosphate concentration culture media. A-E, Relative expression levels of OsSUT1 (A), OsSUT2 (B), OsSUT3 (C), OsSUT4 (D) and OsSUT5 (E). RNA was extracted from rice shoots at the full heading stage. Actin was used as an internal reference. ETRS, Polyphosphate kinase gene (ppk)-expressing transgenic rice with a single-copy line; WT, Wild type; LP, Low inorganic phosphate (Pi) culture medium (15 μmol/L); CP, Normal Pi culture medium (300 μmol/L). Data represent Mean ± SD (n = 3). Different lowercase letters above the bars indicate significant differences between treatments (P < 0.05).

Fig. 6. Mechanism of polyP promoting NSC synthesis and reducing their transport from shoot to root in ETRS in low phosphate concentration culture medium. NSC, Nonstructural carbohydrate; Pi, Inorganic phosphate; SPS, Phosphate synthase.

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