The Expression of TaRca2-α Gene Associated with Net Photosynthesis Rate, Biomass and Grain Yield in Bread Wheat (Triticum aestivum L.) under Field Conditions

Abstract

Improvement in activation of Rubisco by Rubisco activase can potentially enhance CO2 assimilation and photosynthetic efficiency in plants. The three homoeologous copies of TaRca2-α were identified on chromosomes 4AL, 4BS and 4DS (TaRca2-α-4AL, TaRca2-α-4BS, and TaRca2-α-4DS) in bread wheat. Expression patterns of the three copies at heading (Z55), anthesis (Z67) and grain-filling (Z73) stages were investigated through qRT-PCR analyses in a panel of 59 bread wheat genotypes and their effects on net photosynthesis rate (Pn), biomass plant-1 (BMPP) and grain yield plant-1 (GYPP) were further explored. Different but similar expression patterns were observed for the three copies of TaRca2-α at the three growth stages with highest expression at grain-filling stage. TaRca2-α-4BS expressed higher at the three stages than TaRca2-α-4AL and TaRca2-α-4DS. The 59 genotypes could be clustered into three groups as high (7 genotypes), intermediate (41 genotypes) and low (11 genotypes) expression based on the expression of the three copies of TaRca2-α at three growth stages. Significant variations (P<0.01) were observed among the three groups of bread wheat genotypes for Pn, BMPP and GYPP. Generally, the genotypes with higher TaRca2-α expression also showed higher values for Pn, BMPP and GYPP. The expressions of the three copies of TaRca2-α at heading, anthesis and grain-filling stages were positively correlated with Pn, BMPP and GYPP (P<0.01) with stronger association for TaRca2-α-4BS at grain-filling stage. These results revealed that the expression of TaRca2-α contribute substantially to Pn, BMPP and GYPP, and suggested that manipulating TaRca-α expression may efficiently improve Pn, BMPP and GYPP in bread wheat and detecting TaRca-α expression levels with emphasis on TaRca2-α-4BS may be a positive strategy for selection in improving photosynthetic efficiency and grain yield of bread wheat.

Fig 1. Cluster analysis of 59 bread wheat genotypes based on averaged expressions of three copies of TaRca2- α.

Group I: high expression, Group II: intermediate expression; Group III: low expression. The numbers on Y axis represent the codes of 59 wheat genotypes as in Table 1. X axis represents the squared Euclidean distance.

Fig 2. TaRca2-α-4BS expression in flag leaves of the three groups of 59 bread wheat genotypes at Heading (Z55), Anthesis (Z67) and Grain-filling (Z73) stages.

Group I: high expression; Group II: intermediate expression; Group III: low expression. Uppercase letter represent significant differences among the three groups (P≤0.01). The numbers on X-axis correspond to the codes of individual genotypes in Table 1.

Fig 3. Pn (μmol m-2 s-1) of 59 bread wheat genotypes in the three groups at heading (Z55), anthesis (Z67) and grain-filling (Z73) stages.

Group I: high expression; Group II: intermediate expression; Group III: low expression. Uppercase letter represent significant differences (P≤0.01) among the three groups. The numbers on X-axis correspond to the codes of individual genotypes in Table 1.

Fig 4. Regression analysis between the expressions of the three copies of TaRca2-αwith Pn (μmol m^-2 s^-1) at heading, anthesis and grain filling stages.

A: TaRca2-α-4AL; B: TaRca2-α-4BS; C: TaRca2-α-4DS. Pn (Z55), Pn (Z67), Pn (Z73), indicate the Pn at heading (Z55), anthesis (Z67) and grain filling (Z73) stages, respectively.

Fig 5. BMPP and GYPP of bread wheat genotypes in three groups.

Group I: high expression; Group II: intermediate expression; Group III: low expression. Uppercase letters represent significant differences (P<0.01) level. The numbers on X-axis correspond to the codes of individual genotypes in Table 1.

Fig 6. Regression analysis between the expressions of the three copies of TaRca2-α at heading, anthesis and grain filling stages, with BMPP.

A: TaRca2-α-4AL; B: TaRca2-α-4BS; C: TaRca2-α-4DS. Z55, Z67 and Z73, indicate the expression measured at heading (Z55), anthesis (Z67) and grain filling (Z73) stages, respectively.

Fig 7. Regression analysis between the expressions of the three copies of TaRca2-α at heading, anthesis and grain filling stages, with GYPP.

A: TaRca2-α-4AL; B: TaRca2-α-4BS; C: TaRca2-α-4DS. Z55, Z67 and Z73, indicate the expression measured at heading (Z55), anthesis (Z67) and grain filling (Z73) stages, respectively.