Mutualistic Interaction of Piriformospora indica (Serendipita indica) with Aloe vera, the Wonder Plant for Modern Living

Aloe vera, a short-stemmed shrub is described as a “wonder plant”, due to its vast uses in various medical products. Since many decades, extensive research has revealed that the pharmacological active ingredients are distributed in both the gel and rind of the Aloe vera leaves. A. vera is very popular in cosmetic and pharmaceutical industries and it is needed in large quantities with higher fractions of important constituents. To satisfy the market demand, intervention of microbial community seems to be a promising approach, which helps to increase the growth and metabolites along with plant fitness. Piriformospora indica is a root colonizing endophytic fungus, having unique plant growth-promoting properties. It helps the plant to acquire more nutrients from soil even under extreme physical and nutrient stress conditions. It interacts with a wide range of hosts. Interaction of P. indica with A. vera resulted in overall increase in plant biomass and greater shoot and root length, as well as number of shoots and roots as compared to control under both in vitro and in vivo environment conditions. Apart from that, the photosynthetic pigments (Chl a, Chl b and total Chl) and aloin content were observed significantly higher in A. vera plantlets colonized with symbiotic endophyte. The antioxidant activities were also tested and found significantly higher as compared to control plants. This imparts the potential of P. indica, to resist the plants against phyto-pathogenic microbes. P. indica has been proved as a potential candidate to enhance the biomass production along with various value additions in the form of active ingredients in A. vera.


Introduction
Aloe vera is a hardy, perennial, tropical succulent plant with properties like, drought resistant. It belongs to the family Liliaceae which, historically has been used for various medicinal purposes. Genus Aloe contains more than 500 species of flowering succulent plants in the world [1]. The size of these plants varies from an inch to two feet or more in diameter. These plants are highly complex in shape and spread out colonies consisting of thousands of plants. Many Aloe species are scattered naturally in North Africa. Among 500 species, most commonly occurring species of A. vera is Aloe barbadensis [2].
A. vera is generally cultivated in moderate environments rather than chilling, such as tropical or sub-tropical regions. Another beauty of this plant is blooming; some older plants bloom and produce beautiful flowers with tall stock covered by bright color petals.
Aloe vera, a short-stemmed shrub is described as a "wonder plant", due to its frequent use in various medical products. The gel obtained from the plant's leaves has been used in many pharmaceutical products ( Figure 1). The medicinal properties are well documented in various Indian indigenous system of medicine like Ayurveda, Siddha, Unani and Homeopathy [3]. Extensive research since last decades has revealed that the pharmacologically active ingredients are distributed in both the gel and rind of the A. vera leaves. A. vera is very popular in cosmetic and pharmaceutical industries [3] [4].
Different products from A. vera gel which are commercially available in the market are depicted in Figure 2.
A. vera is very popular in skin care markets due to its cooling effect, which protects skin from long time exposure of sun light [2] [4]. It helps in eliminating skin diseases like acne and eczema ( Figure 3). Aloe is also marketed as a remedy for ulcer, diabetes, cancer, arthritis, cough, wound and immune disorders. It has been proven as an effective antiseptic, powerful detoxifier and tonic for the nervous system [5].
Aloe flowers are usually tubular or trumpet-shaped and are arranged in clusters and their fruit is capsular. There are more than 20 species of aloe and their number is growing steadily, as new hybrids are constantly being created. The acíbar, a yellowish liquid layer present between the skin of penca and the gel of Aloe vera is composed of aloin. It is bitter in taste and by boiling, it is transformed   into a dark brown amorphous mass. Garcia

Mechanism of Actions
Wound healing: A mannose-rich polysaccharide, Glucomannan and a growth hormone, gibberellin, interacts with growth factor receptors at the fibroblast. Then it stimulates its activity and proliferation, which in turn notably increases collagen synthesis after oral intake. Aloe gel helps in increasing the collagen content on the wound which facilitates the penetration of other constituents inside the skin tissue [2] [4] [7]. It speeds up the wound contraction and accelerated the process of ensuing scar tissue. An increased synthesis of dermatan sulphate and hyaluronic acid in the granulation tissue of a healing wound accelerated the process of curing the wound [6] [9].
Anti-aging effects: Mucopolysaccharides present in skin tissue helps in binding moisture. A. vera sap/gel stimulates fibroblast cells which produces the elastin fibers and collagen. These two makes the skin pores less elastic and makes the skin tight and less wrinkled. Additionally, Aloe has cohesive properties which binds with the superficial epidermal tissue and stick them together and American Journal of Plant Sciences softens the skin. Another important mineral Zinc, an astringent helps to tighten the skin pores. Amino acids help in softening the hardened skin cells and nourish the skin cells. Due to its moisturizing effect A. vera has been extensively studied in the field of treatment of dry skin. It has been proven Aloe gel improved the skin integrity, reduces wrinkles and decreases erythema. Apart from these effects aloe gel also shows anti-acne impact [2]

Piriformospora indica: A Mutualistic Plant Growth Promoter
P. indica is root colonizing endophytic fungus, extensively studied since last two decades due to its unique plant growth promoting properties. It helps plant to acquire more nutrients from soil even under extreme physical and nutrient stress conditions [11] [12]. It interacts with a wide range of hosts, including bryophytes, pteridophytes, gymnosperms and cruciferiae and large number of mono and dicot plants [13]. The fungus promotes nutrient uptake, allows plants to survive under water, temperature and salt stresses, and confers systemic resistance to toxins, heavy metal ions, insects and pathogenic organisms. Further, it is shown to stimulate excessive production of biomass, early flowering, seed production and a potential microorganism imparting biological hardening to tissue culture-raised plants [11] [12] [14] [15] ( Figure 5).

P. indica Promotes Growth of Aloe vera with Value Additions
The study had been undertaken to investigate the effect of endophyte P. indica on the physiological growth and the essential phytochemical contents of A. vera.
The results showed overall increase in plant biomass and greater shoot and root length as well as number of shoots and roots as compared to control under both in vitro and in vivo environment conditions ( Figure 6). Apart from that the photosynthetic pigment (Chl a, Chl b and total Chl) and gel content were  observed significantly higher (93.45%, 101.61%, and 60.46% respectively) in symbiotic fungus inoculated A. vera plantlets [16] [17].
The interaction study of medicinal plant with P. indica was conducted at large scale in bio hardening faculty at Amity University Noida, India ( Figure  7).
The root colonization study with P. indica showed 67.5% colonization in A. vera roots. The percentage of colonization inside the root of plants showed the affinity of host-symbiont relationship. This colonization resulted in 16.5% increment in gel content along with 100% survival rate of colonized plants. This gel content has a great commercial importance to cosmetics and medicine industries as described earlier in this article. P. indica treated plantlets also had 52.53% higher aloin content as compared to the control plantlets. The aloin content as determined by HPLC was found to be 1.28 ± 0.057 mg aloin/g of leaf exudate for the treated and 0.844 ± 0.001 for the control set, marking an overall increase of 52.23%. This aloin is a potential anticancer agent and used as a laxative. These have various therapeutic properties and are used frequently in recovery from radiation damage and wound healing etc. [16].

P. indica Facilitates Nutrient Supply and Activates Various Biological Pathways
Our laboratory at Amity University, Noida first time successfully performed the interaction study of P. indica with A. vera under in vitro conditions. After successful colonization of P. indica, it facilitates the transfer/supply of nutrients like nitrogen and phosphorus to the roots of host plant which stimulates the cascade of biological reactions to synthesize various proteins, which participated in growth promotion of plant, enhancement of secondary metabolites, boosting immune system to trigger the defense mechanism against various biotic and abiotic stresses to increase the plant fitness [13] [19].

Conclusion
P. indica is considered as a potential candidate to enhance the biomass production along with various value additions in the form of active ingredients. It significantly increases the vegetative growth of plant and boost immunity to sustain in diverse environment as compared to control. The pharmaceutically important metabolites were also found increased many folds in fungal treated A. vera host.

Future Prospects
The study proves the future prospective of P. indica being used as biopriming agent for achieving better growth, better survival rate along with enhanced growth of in vitro raised plantlets along with substantial enhancement of secondary metabolites. The mechanism involved in interaction with mycobiont American Journal of Plant Sciences with host needs to be elucidated to understand the physiology behind this phenomenon.