MYB Transcription Factor OsC1 Involves the Regulation of Purple Leaf Sheath in Rice

Although several regulators associated with purple traits in rice have been identified, the genetic basis of the purple sheath remains unclear. In the present study, F2-1 and F2-2 populations were constructed using purple sheath (H93S) and green sheath (R1173 and YHSM), respectively. In order to identify QTL loci in purple sheaths, BSA analyses were performed on the two F2 populations. A crucial QTL for purple sheath was identified, tentatively named qPLSr6, and was located in the 4.61 Mb to 6.03 Mb region of chromosome 6. Combined with expression pattern analysis of candidate genes, LOC_Os06g10350 (OsC1) was suggested as a candidate gene. The homozygous mutant KO-1 and KO-2 created through CRISPR/Cas9 editing, lost their purple leaf sheath. The RT-PCR revealed that OsC1, anthocyanin synthase (ANS), diflavonol-4-reductase (DFR), flavanone-3-hydroxylase (F3H), and flavanone-3'-hydroxylase (F3'H) expression levels were dramatically down-regulated in the mutants. The yeast report system indicated that the 145-272 aa region at the C-terminal of OsC1^PLSr is a positive transcriptional activation domain. The results indicated that OsC1^PLSr synthesized anthocyanins by regulating the expression of ANS, DFR, F3H, and F3'H. This study provides new insights into the genetic basis of the purple sheath.