Functional Characterization of an Anthocyanidin Reductase Gene from the Fibers of Upland Cotton (Gossypium Hirsutum)

Metabolic profiling, gene cloning, enzymatic analysis, ectopic expression, and gene silencing experiments demonstrate that the anthocyanidin reductase (ANR) pathway is involved in the biosynthesis of proanthocyanidins in upland cotton. Proanthocyanidins (PAs) are oligomeric or polymeric flavan-3-ols, however, the biosynthetic pathway of PAs in cotton remains to be elucidated. Here, we report on an anthocyanidin reductase (ANR) gene from cotton fibers and the ANR pathway of PAs. Phytochemical analysis demonstrated that leaves, stems, roots, and early developing fibers produced PAs and their monomers, including (-)-epicatechin, (-)-catechin, (-)-epigallocatechin, and (-)-gallocatechin. Crude PA extractions from different tissues were boiled in Butanol:HCl. Cyanidin, delphinidin, and pelargonidin were produced, indicating that cotton PAs include diverse extension unit structures. An ANR cDNA homolog (named GhANR1) was cloned from developing fibers. The open reading frame, composed of 1,011 bp nucleotides, was expressed in E. coli to obtain a recombinant protein. In the presence of NADPH, the recombinant enzyme catalyzed cyanidin, delphinidin, and pelargonidin to (-)-epicatechin and (-)-catechin, (-)-epigallocatechin and (-)-gallocatechin, and (-)-epiafzelechin and (-)-afzelechin, respectively. The ectopic expression of GhANR11 in an Arabidopsis ban mutant allowed for the reconstruction of the ANR pathway and PA biosynthesis in the seed coat. Virus-induced gene silencing (VIGS) of GhANR11 led to a significant increase in anthocyanins and a decrease in the PAs, (-)-epicatechin, and (-)-catechin in the stems and leaves of VIGS-infected plants. Taken together, these data demonstrate that the ANR pathway contributes to the biosynthesis of flavan-3-ols and PAs in cotton.