Proanthocyanidin biosynthesis in the developing wheat seed coat investigated by chemical and RNA‐Seq analysis

Abstract

The composition of proanthocyanidins in the testa (seed coat) of bread wheat was analyzed by thiolysis of PA oligomers from developing grain and found to consist of (+)‐catechin monomers, with a small amount of (+)‐gallocatechin. The average chain length of soluble PA stayed relatively constant between 10 and 20 days post‐anthesis, whereas that of unextractable PA increased over the same period, suggesting that increases in chain length might account for the insolubility of PAs from mature wheat grain. We carried out RNA‐Seq followed by differential expression analysis from dissected tissues of developing grain from red‐ and white‐grained near‐isogenic lines differing in the presence of an active R gene that encodes a MYB transcription factor involved in control of PA biosynthesis. In addition to genes already identified encoding chalcone synthase, chalcone isomerase, flavanone 3‐hydroxylase, and dihydroxyflavonoid 4‐reductase, we showed that wheat genes encoding phenylalanine ammonia lyase, flavonoid 3′,5′‐hydroxylase, leucoanthocyanidin reductase, and a glutathione S ‐transferase (the orthologue of maize Bronze‐2 ) were more highly expressed in the red NIL. We also identified candidate orthologues of other catalytic and regulatory components of flavonoid biosynthesis in wheat.

An unconventional proanthocyanidin pathway in maize

“…In the apparent absence of an efficient polymerization system, the operation of an ANR that generates the 2,3-trans-flavan-3,4-diol, and a route to catechin-cysteine via 2,3-trans-leucocyanidin, the major products are isomers of procyanidins B2 and B4, along with catechin-anthocyanin conjugates. The recent publication of a set of candidate PA biosynthesis genes expressed in the seed coat of wheat 51 , which naturally accumulates (+)-catechin type PAs, will facilitate comparative approaches to deciphering the key controlling steps in PA biosynthesis in cereals. Engineering PAs in maize represents a promising strategy for producing value-added agricultural products and for improving the health benefits of maize for humans and livestock, and understanding the unconventional endogenous pathway in maize sets the stage for this purpose.…”

Stacked mutations in wheat homologues of rice SEMI-DWARF1 confer a novel semi-dwarf phenotype

“…For this work, an M 2 population of 2,150 lines, each derived from an individual M 1 plant, was grown; leaf material and M 3 seeds were collected from the 2,057 fertile plants. Plant cultivation and propagation was as previously described [ 31 ] and DNA was extracted from 3–5 g leaf tissue samples [ 32 ]. Field experiments included wild-type ‘Cadenza’ and a line containing an introgressed Rht-D1b semi-dwarfing allele in the ‘Cadenza’ background described previously [ 12 ].…”

“…There were too few individuals to distinguish between the backcrossing streams for each triple mutant so analysis was carried out on data combined from the different streams. Up to 10 replicates of each line were germinated on damp filter paper, transferred to 2 cm × 2 cm cells of Rothamsted Prescription Mix compost with added nutrients [ 31 ] and subsequently moved to 15 cm pots in a randomised block design.…”

Tartary Buckwheat (Fagopyrum tataricum) FtTT8 Inhibits Anthocyanin Biosynthesis and Promotes Proanthocyanidin Biosynthesis

“…The anthocyanin biosynthesis pathway is one branch of the flavonoid biosynthesis pathway, which includes chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol-4-reductase (DFR), anthocyanidin synthase (ANS), and anthocyanin 3-O-glucosyltransferase (UFGT). In this pathway, two substrates, leucoanthocyantin and anthocyanidin, are catalyzed by leucoanthocyanin reductase (LAR) and anthocyanidin reductase (ANR), respectively, which leads to the biosynthesis of proanthocyanidins (PAs), another kind of flavonoid and contributes to the pigmentation of the plant's seed coat [20][21][22]. Nowadays, the biosynthesis pathway and regulation mechanism of anthocyanin and PA have been well established and deeply characterized in model plants Arabidopsis thaliana [23][24][25], Petunia hybrida [26,27], Zay maize [28,29], as well as other plant species.…”