Rice gene, BBH/Lsi1, regulates the color of rice hull by reducing the absorption and deposition of silicon and accumulating excess flavonoid

Abstract

The color of grain hull is one of the remarkable traits which can be easily identified after heading, especially at the mature stage. In present study, a discoloration hull mutant named black–brown hull (bbh), was obtained from an indica cultivar Zhenong 34 by mutagenesis with ethyl methane sulfonate (EMS). The hull color of bbh mutant initially appeared black–brown on the 15th day and became completely black–brown on the 30th day after heading. The root of bbh was shorter than that of WT during the whole growth period. Furthermore, the total flavonoids content in the hulls and the silicon deposition in the leaves of bbh were both remarkably higher than WT. The results of map-based cloning indicated that the mutant trait of bbh was controlled by a single recessive nuclear gene, which was located on the long arm of chromosome 2 with a physical distance of 64.9 kb. The comparison of gDNA sequence between bbh and WT showed that there was a substitution from T to C (+ 2360) in the third exon of LOC_Os02g51110. BBH was an allelic gene of Lsi1, which encoded a water channel protein (aquaporin) involving in silicon uptake. The expression levels of the genes related to silicon absorption, transportation and distribution were detected to be up- or down-regulated at different stages in bbh root. Moreover, the transcripts of structural enzymatic genes involved in flavonoid biosynthesis in hulls also had apparent differences between WT and bbh mutant. Above all, the results revealed that BBH/Lsi1 was responsible to the black–brown hull by reducing the absorption and deposition of silicon and accumulating overmuch flavonoid.