Assessment of antioxidant properties in selected pigmented and non-pigmented rice (Oryza sativa L.) germplasm and determination of its association with Rc gene haplotypes.

Background: Antioxidant properties of rice provide various health benefits due to its ability to inhibit cellular oxidation. Antioxidant content of rice is known to be linked with the pericarp pigmentation. The Rc gene of rice (Os07g0211500) codes for a basic helix-loop-helix (bHLH) protein, acting as a transcriptional factor in regulating proanthocyanidin biosynthesis. The current study was carried out to evaluate the variation of antioxidant properties in a selected panel of rice accessions and assess the possibility of using haplotypes defined based on the Rc gene to predict pericarp pigmentation and antioxidant content in rice.

Results: Thirty-two rice accessions were evaluated for grain pericarp colour and antioxidant properties; total phenolic content (TPC), total flavonoids (TFC), proanthocyanidins (PAC) and radical scavenging activity (RSA). The parameters TPC, TFC and PAC showed significant positive correlation with RSA (r > 0.69; P < 0.01). The study panel showed a wide variation for antioxidant properties and rice accessions such as Sudu Heenati, Deweraddiri, Madathawalu, Masuran, Ld 368, At 311, Kalu Heenati, Bw 272-6B, Pokkali, At 362 and Wanni Dahanala exhibited profound potential with respect to antioxidant properties. Based on three-target sites previously reported as critical for the function of the coded bHLH protein (an A/C SNP at 1,353-bp, a 1-bp insertion/deletion at 1,388-bp, and a 14-bp insertion/deletion at 1,408-1,421-bp positioned in the mRNA corresponding to the exon 6 of rice Rc gene), three haplotypes were defined (H1-H3). Pigmentation of the rice pericarp could be successfully explained based on the defined haplotypes (H1 (C/G/+): red, and H2 (A/G/+) and H3 (C/G/-): white), and the H1 haplotype corresponded to a significantly (P < 0.05) higher TPC, TFC, PAC and RSA compared to the other haplotypes.

Conclusions: The studied rice accessions showed a significant variation with respect to antioxidant properties. Haplotype H1 defined based on the three-target sites in the exon 6 of Rc gene can detect rice accessions with red pigmented pericarp and high antioxidant properties effectively. Hence, its use can be recommended as an alternative to biochemical assays for screening during rice breeding programs.