AUTHOR=Tetreault Hannah M. , Gries Tammy , Liu Sarah , Toy John , Xin Zhanguo , Vermerris Wilfred , Ralph John , Funnell-Harris Deanna L. , Sattler Scott E. 

TITLE=The Sorghum (Sorghum bicolor) Brown Midrib 30 Gene Encodes a Chalcone Isomerase Required for Cell Wall Lignification

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.732307

DOI=10.3389/fpls.2021.732307

ISSN=1664-462X

ABSTRACT=<p>In sorghum (<italic>Sorghum bicolor</italic>) and other C<sub>4</sub> grasses, <italic>brown midrib</italic> (<italic>bmr</italic>) mutants have long been associated with plants impaired in their ability to synthesize lignin. The <italic>brown midrib 30</italic> (<italic>Bmr30</italic>) gene, identified using a bulk segregant analysis and next-generation sequencing, was determined to encode a chalcone isomerase (CHI). Two independent mutations within this gene confirmed that loss of its function was responsible for the brown leaf midrib phenotype and reduced lignin concentration. Loss of the <italic>Bmr30</italic> gene function, as shown by histochemical staining of leaf midrib and stalk sections, resulted in altered cell wall composition. In the <italic>bmr30</italic> mutants, CHI activity was drastically reduced, and the accumulation of total flavonoids and total anthocyanins was impaired, which is consistent with its function in flavonoid biosynthesis. The level of the flavone lignin monomer tricin was reduced 20-fold in the stem relative to wild type, and to undetectable levels in the leaf tissue of the mutants. The <italic>bmr30</italic> mutant, therefore, harbors a mutation in a phenylpropanoid biosynthetic gene that is key to the interconnection between flavonoids and monolignols, both of which are utilized for lignin synthesis in the grasses.</p>