**The Flavonol-Anthocyanin Pathway in Blackberry and Arabidopsis: State of the Art**

Enrique Gutierrez, Ana García‐Villaraco Velasco,

Jose Antonio Lucas, F. Javier Gutierrez‐Mañero and

Beatriz Ramos‐Solano

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67902

#### **Abstract**

Flavonols and anthocyanins are plant secondary metabolites with an increasing interest due to their beneficial effects on human health. They are present in all plants, participat‐ ing in plant protection against biotic and abiotic stresses. However, only some plant spe‐ cies accumulate them in relevant amounts, as is the case for berries. Among the health benefits reported is prevention of metabolic syndrome, s, including prevention of insulin resistance associated to type 2 diabetes. Therefore, there is a big interest to improve contents on plant foods to benefit health through the diet, as well as to obtain them for functional ingredients for food supplements. In fulfillment of this objective, a deep study about their biosynthetic pathway has been carried out in model plants, where the genome is available. However, not all species that accumulate them in high amounts have their genome sequenced, as is the case for blackberry. Transcriptomic approaches have been undertaken to gain knowledge of its specific biosynthetic pathway and regulatory ele‐ ments, aiming to improve bioactive contents in the edible parts. Furthermore, determin‐ ing the regulatory pathways will help to improve yields and in vitro production. For this purpose, a review on elicitors used to trigger this pathway is presented.

**Keywords:** flavonols, anthocyanins, blackberry, Rubus, Arabidopsis, elicitors, transcription factors (MYB)

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

Blackberry fruits are an important source of bioactive compounds, among which are fla‐ vonols, anthocyanins, and catechins. These compounds exhibit beneficial effects on human health, which is the main reason they have become so popular nowadays, especially because they are easy to include in diets, at least in developed countries where incidence of patholo‐ gies is high. Among these health benefits are their general antioxidant effects, as all these compounds can scavenge reactive oxygen species (ROS), anti-inflammatory and antimicro‐ bial effect, glucose metabolism, and leukocyte migration (effects in both inflammation and cancer) [1, 2]. Catechins and anthocyanins have also proved their ability to improve endothe‐ lial function, hypertension, coronary heart disease, obesity, insulin resistance, as well as glu‐ cose and lipid metabolism [3, 4]. Hence, including blackberry on human diet is beneficial for health, since a high content in flavonoids has been reported, and, in addition to its beneficial effects, it lacks adverse or secondary effects. Moreover, these compounds are also responsible for major organoleptic, nutritive, and processing characteristics of feed, food, and beverages, and impact many agronomical crop traits [5, 6].

In addition to the relevance for human health, flavonols, anthocyanins, and catechins play a key role on plant physiology. As secondary metabolites, they play a wide variety of functions, mainly helping the plant to adapt to the environment, among which the following have been reported, namely (i) UV radiation and oxidative stress protection, (ii) pathogen interactions (pathogen resistance), (iii) protection from herbivore, (iv) allelopathy, (v) nodulation (symbi‐ osis), (vi) auxin transport, and (vii) they also attract different organism for pollination because of the color of the flower [1, 7, 8].

Despite the agricultural and biological importance of the genus *Rubus*, knowledge of their genetics and genome is very limited. Hence, in order to gain knowledge about the metabo‐ lism of these compounds, different approaches need to be undertaken, including the physi‐ ological, metabolic, and transcriptomic levels. One of the most important factors affecting the quality of the fruit is its content in phenolic compounds [6]. The synthesis of these com‐ pounds mainly depends on the phenylpropanoid and its derivative pathways, which starts with the phenylalanine, as many others (**Figure 1**). Furthermore, validation of the mecha‐ nisms controlling this biosynthetic pathway needs to be referred to model plants; among which, the most commonly used is *Arabidopsis thaliana.* However, the use of Arabidopsis is limited since it lacks edible fruits, so for studies related to fruits, either strawberry or tomato is used as reference.

*Rubus* sp. is a woody plant that belongs to *Rosaceae* family, in which other plants such as straw‐ berry (*Fragaria vesca* L.), raspberry (*Rubus idaeus* L.), cherry tree (*Prunus avium* L.), or apple (*Malus domestica*) among others are enclosed; all of them belong to a wide group of plants commonly called *berries*. They are known because of their high accumulation of secondary metabolites in the fruit, which behave as functional components, beneficial for human health. Those compounds are mainly polyphenols like flavonols, anthocyanins, and catechins, strong natural antioxidants [9–11].

**Figure 1.** Phenylpropanoid pathway.

**1. Introduction**

130 Flavonoids - From Biosynthesis to Human Health

and impact many agronomical crop traits [5, 6].

of the color of the flower [1, 7, 8].

is used as reference.

natural antioxidants [9–11].

Blackberry fruits are an important source of bioactive compounds, among which are fla‐ vonols, anthocyanins, and catechins. These compounds exhibit beneficial effects on human health, which is the main reason they have become so popular nowadays, especially because they are easy to include in diets, at least in developed countries where incidence of patholo‐ gies is high. Among these health benefits are their general antioxidant effects, as all these compounds can scavenge reactive oxygen species (ROS), anti-inflammatory and antimicro‐ bial effect, glucose metabolism, and leukocyte migration (effects in both inflammation and cancer) [1, 2]. Catechins and anthocyanins have also proved their ability to improve endothe‐ lial function, hypertension, coronary heart disease, obesity, insulin resistance, as well as glu‐ cose and lipid metabolism [3, 4]. Hence, including blackberry on human diet is beneficial for health, since a high content in flavonoids has been reported, and, in addition to its beneficial effects, it lacks adverse or secondary effects. Moreover, these compounds are also responsible for major organoleptic, nutritive, and processing characteristics of feed, food, and beverages,

In addition to the relevance for human health, flavonols, anthocyanins, and catechins play a key role on plant physiology. As secondary metabolites, they play a wide variety of functions, mainly helping the plant to adapt to the environment, among which the following have been reported, namely (i) UV radiation and oxidative stress protection, (ii) pathogen interactions (pathogen resistance), (iii) protection from herbivore, (iv) allelopathy, (v) nodulation (symbi‐ osis), (vi) auxin transport, and (vii) they also attract different organism for pollination because

Despite the agricultural and biological importance of the genus *Rubus*, knowledge of their genetics and genome is very limited. Hence, in order to gain knowledge about the metabo‐ lism of these compounds, different approaches need to be undertaken, including the physi‐ ological, metabolic, and transcriptomic levels. One of the most important factors affecting the quality of the fruit is its content in phenolic compounds [6]. The synthesis of these com‐ pounds mainly depends on the phenylpropanoid and its derivative pathways, which starts with the phenylalanine, as many others (**Figure 1**). Furthermore, validation of the mecha‐ nisms controlling this biosynthetic pathway needs to be referred to model plants; among which, the most commonly used is *Arabidopsis thaliana.* However, the use of Arabidopsis is limited since it lacks edible fruits, so for studies related to fruits, either strawberry or tomato

*Rubus* sp. is a woody plant that belongs to *Rosaceae* family, in which other plants such as straw‐ berry (*Fragaria vesca* L.), raspberry (*Rubus idaeus* L.), cherry tree (*Prunus avium* L.), or apple (*Malus domestica*) among others are enclosed; all of them belong to a wide group of plants commonly called *berries*. They are known because of their high accumulation of secondary metabolites in the fruit, which behave as functional components, beneficial for human health. Those compounds are mainly polyphenols like flavonols, anthocyanins, and catechins, strong *Rubus* L. genus is composed of 600–800 species approximately, distributed all around the world in very different habitats, and classified into 12 different subgenus that are in turn divided into different groups. The most abundant species in Europe is the *Rubus* spp. subge‐ nus (Eubatus Focke) that is divided in more than 130 species; their natural habitat and distri‐ bution is in the woods (**Table 1**).


**Table 1.** *Rubus* subgenus.

Plants that belong to the subgenus *Rubus* spp. are typical wild species and are usually hand‐ picked in the season. However, since it became an important plant for agriculture, there has been an increasing interest in improving the size of the fruit, the organoleptic properties, fruit yield, and get rid of the thorns, since they constitute a nuisance for harvest. To achieve these objectives, classic crossbreeding has resulted in development of many commercial varieties to favor a given trait that benefits production in each geographical location. Among these cultivars are "Ashton Cross" that is vigorous and thorny, "Bedford Giant" that in addition to these two traits shows a good yield; "Black satin," also vigorous but thornless; "thornless evergreen" that provides a thornless plant, high yield and high quality fruits; "Fantasia" that produces very large fruits and finally in this shortlisted group is "Loch Ness," that is a thorn‐ less cultivar with very large fruits and semierect canes, which is the cultivar used in this study (**Table 2**) [12].

*Rubus* spp. Var. Loch Ness is a high yielding thornless tetraploid (4*n* = 28) blackberry, and one of the most widely cultivated varieties. However, despite its high-added economic value and as a source of bioactive compounds, its genome has not been sequenced yet. Therefore, other strategies need to be used to gain knowledge of the production and health-related benefits.

The aim of this chapter is to review the literature about blackberry and report the state of the arts about this plant species. As the genome is not reported, data about the core genes in the biosynthetic pathway as well as regulatory genes are referred to as the model plant *A. thaliana*. Also, structure of the bioactives which is responsible for health benefits as well


**Table 2.** Phenolic compound contents of thorny and thornless blackberries (mg/100g FW) [13].

as their qualitative and quantitative composition in berry fruit and in model plant are pre‐ sented, so a relationship between composition and core and regulatory genes description is envisaged and vice versa. Finally, the physiological role of these secondary metabolites for plants is also presented, and finally highlights the relevance of this pathway of plant second‐ ary metabolism, as well as its biotechnological potential.
