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Rc Gene Sequence and Expression Evaluation in a Red-Kernel Rice Genotype

Barbara Ferrari

Most cultivated rice is white all over the world; however, pigmented rice varieties could be preferable, as they have the potential to promote human health because containing antioxidative compounds inhibiting/reducing reactive cell-damaging free radicals-even if few in vivo studies have been reported about bioactivity of red rice on humans. Previous studies demonstrated that, generally, dehulled red rice shows a total antioxidant activity more than three times greater than dehulled white rice, due to the presence of proanthocyanidins, which accumulate as colourless compounds during the early steps of maturation and subsequently give the seed its pigmentation after oxidative reactions along maturation and desiccation process. Rc gene, which codifies for a bHLH (basic helix-loop-helix) protein responsible for proanthocyanidins’ accumulation into the inner seed coat below the pericarp, was here studied from the point of view of expression, developing and applying a qRT-PCR (quantitative reverse transcription polymerase chain reaction) assay to all the grain filling phases. Results showed that proantocyanidins are present into the caryopses since the milky stage. This study confirmed the key role of the 14bp deletion in Rc-bHLH in the suppression of rice pigmentation and precisely showed that the maximum Rc gene expression was detected at an early stage of grain-filling, i.e., at the elongation period. Moreover, starting from this specific knowledge of the Rc expression timing, targeted highthroughput experiments (transcriptomics and RNA-seq) could be greatly facilitated for expression analyses in seeds of all pigmented rices and presumably of different small grain cereals.