Anthocyanin Production in Grape Berry Skins

This is a follow up blog to my recent blog Why is Red Wine Colored Red. Now I'm going to get into the weeds regarding the genes that control anthocyanin production. In the previous blog, I wrote that anthocyanin production begins with the amino acid phenylalanine and the main point of control of anthocyanin production in the grape berry is after leucoanthocyanidin dioxygenase or LDOX. The committed step for anthocyanin production was dependent upon the enzyme UDP glucose flavonoid 3-o-glucosyl transferase or UFGT. UFGT was only detected in the berry skin and was always associated with anthocyanin accumulation.
Some elegant work done by Boss et al. in 1996 using Shiraz showed the expression of the Flavonoid Pathway genes in the following grapevine locations:

• Young leaf
• Mid leaf
• Old leaf
• Tendril
• Green cane
• Root
• Seed
• Flower
• Berry skin
• Berry flesh

Boss et al. used the northern blot to show the expression of the mRNA that code for the enzymes involved in the conversion of the substrates in the Flavonoid Pathway. By comparing the schematic of the anthocyanin pathway on the left with the Northern blot analysis on the right, it is clear that anthocyanin is produced only in the grape berry skin.

With the exception of Teinturier Grape Varieties, whose flesh is also colored red, red grape varieties of contain anthocyanins only in their skins.
References:
1. Boss PK, Davies C, Robinson SP, Expression of anthocyanin biosynthesis pathway genes in red and white grapes, Plant Mol Biol., 1996, Nov32(3):565-9.
2. Douglas Adams, VI257, Lesson 8, pg. 23.
3. Boss P, Davies C, Robinson S (1996b), "Expression of anthocyanin biosynthesis pathway genes in red and white grapes", Plant Mol Biol, 32:565 - 569.
4. Lijavetzky et al., 2006, Mol. Genet. Genomics, 2006: 427-435.
5. José Tomás Matus, Felipe Aquea and Patricio Arce-Johnson, BMC Plant Biology, 2008, 8:83.

General Phenylpropanoid/Flavonoid Pathway

On February 16th, I blogged about Why is Red Wine Colored Red and in that blog, I included this schematic of the pathway to anthocyanins that began with the amino acid phenylalanine:¹

I then found a diagram that showed a more complete schematic of the flavonoid pathway after it diverges at the point of the reaction involving 4-coumaroyl-CoA. By looking at the schematic above and comparing it to the schematic below, the point of synthesis of the three main flavonoid classes flavonols, anthocyanins, and flavan-3-ols can be discerned.²

Flavan-3-ol monomers include (+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin-3-O-gallate, and traces of (+)-gallocatechin. The oligomers and polymers of these flavan-3-ol monomers, are the most abundant flavonoids found in berries.
Why is this important:

• the most abundant flavonoids are proanthocyanidins (PAs)
• the major quality determinants for fruit and wine are the proanthocyanidins
• the total content of PAs is usually higher in seeds
• large quantities of (-)-epicatechin-3-O-gallate are located in the seeds
• the polymer size of PAs is much larger in the skin with (-)-epigallocatechin being a major skin PA subunit

References:
1. Boss PK, Davies C, Robinson SP, Expression of anthocyanin biosynthesis pathway genes in red and white grapes, Plant Mol Biol., 1996, Nov32(3):565-9.
2. Yung-Fen Huang, Sandrine Vialet, Jean-Luc Guiraud, Laurent Torregrosa, Yves Bertrand,Veronique Cheynier, Patrice This and Nancy Terrier, A negative MYB regulator of proanthocyanidin accumulation, identified through expression quantitative locus mapping in the grape berry, New Phytologist, (2014) 201: 795–809 doi: 10.1111/nph.12557.

2015 Paumanok Minimalist Chenin Blanc

Recently, we drank this 2015 Minimalist Chenin Blanc from Paumanok. We purchased this bottle from Paumanok when we went to visit Kareem and Charles Massoud with our own version of Chenin Blanc that we made from our harvest in 2015. It was very interesting to compare 4 different styles of Chenin Blanc. We brought over our 2015 Chenin Blanc Sec and our 2015 Chenin Blanc Sussreserve. We compared it with the 2015 Paumanok Chenin Blanc and the 2015 Paumanok Minimalist Chenin Blanc. I really enjoyed the Minimalist and tasted the stone fruit spectrum of apricots and peaches.

Why is Red Wine Colored Red

Have you ever wondered why red wine is colored red? I wrote about it in a blogpost called Anthocyanins Give Red Wine Their Color. The red color in grapes is attributable to the anthocyanins located in the grape berry skin.¹
I'm going to delve a little deeper in this blog about how anthocyanins are formed and why they end up being accumulated in the berry skin. The pathway for the formation of anthocyanins begins with the amino acid phenylalanine:²

In the diagram shown above, phenylalanine can be shunted into two pathways:

• General Phenylpropanoid Metabolic Pathway: Phenylalanine is first converted to 4-coumaroyl-CoA and this compound may be used in the production of lignins, coumarins and stilbenes
• Flavonoid Pathway: Conversion of 4-coumaroyl-CoA results in the production of a range of flavonoid compounds, the most common being aurones, flavones, flavonols, isoflavonoids, proanthocyanidins and anthocyanins.

The main point of control of anthocyanin production in the grape berry is after leucoanthocyanidin dioxygenase or LDOX. Expression of the enzyme that converts the precursor of anthocyanins, UDP glucose flavonoid 3-o-glucosyl transferase or UFGT was only detected in the berry skin and was always associated with anthocyanin accumulation. Red wines therefore, are the result of the extraction of anthocyanins from the grape berry skins and oh so much more chemistry! (Maybe in another blog)

References:
1. Douglas Adams, VI257, Lesson 8, pg. 23. All structures were drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.
2. Boss P, Davies C, Robinson S (1996b), "Expression of anthocyanin biosynthesis pathway genes in red and white grapes", Plant Mol Biol, 32:565 - 569.
3. Lijavetzky et al., 2006, Mol. Genet. Genomics, 2006: 427-435.
4. José Tomás Matus, Felipe Aquea and Patricio Arce-Johnson, BMC Plant Biology, 2008, 8:83.
5. A negative MYB regulator of proanthocyanidin accumulation, identified through expression quantitative locus mapping in the grape berry, New Phytologist, (2014) 201: 795–809 doi: 10.1111/nph.12557.