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Fungal manipulation of plant development
Plants and fungi have developed a complex system symbiosis which can be categorized as commensalistic,mutualistic or parasitic. Symbiotic fungi typically form associations that are mutualistic or pathogenic depending on the species of fungal symbiont interacting with corresponding host plant. Symbiotic mycorrhizal associations that are mutualistic increase nutrient availability for the host plant in return for carbon and other essential nutrients needed to thrive for the fungus. Besides aiding in nutrient availability the interacting fungi also plays a role in plant development by the production and manipulation of plant hormones. The manipulation of hormones causes morphological changes in the plant which can be beneficial (mutualistic) or detrimental (parasitic) to the plant.

Lateral root growth
Auxin is a plant hormone that promotes cell growth and root production, making it a target hormone for fungi to manipulate. Fungi have the ability to increase auxin-gene expression and increase auxin production. An increase in auxin promotes both lateral root formation and growth. Fungi control auxin-gene expression by increasing beta-glucuronidase (GUS) activity in the xylem pole pericycle founder cells of the plant root. An increase in GUS activity promotes a higher expression of auxin transporter cells in the plant causing an increase in delivery of auxin acropetally and stimulates lateral root production. The production of auxin by fungi increases the auxin levels in the plant root which also stimulates lateral root growth via the auxin transport mechanism of the plant.

Root hairs
Ethylene is another plant hormone that contributes to plant development such as root initiation, leaf senescence and fruit ripening. Fungi have the ability to produce ethylene which in turn promotes root hair growth. An increase in root hair growth allows for greater plant exploration of the soil and an increase in nutrient uptake as well. Various mechanisms as to how fungal produced ethylene stimulates root hair growth have been proposed, but not yet well defined. One of the suggested mechanism is that the fungus produces α-Keto-γ-(methylthio)butyric acid (KMBA) which is then degraded into ethylene via light and taken up by the plant. Along with ethylene, auxin too can increase root hair length. Ethylene can also regulate auxin transport positively by increasing the expression of auxin transport ultimately leading to higher auxin concentration which stimulates root hair formation and lateral root growth.

Leaves
Gibberellin is a plant hormone that plays a major role in seed germination, leaf expansion and induction of flowering. Fungi also have the ability to produce gibberellin. Greater concentrations of gibberellin at the root of the host plant has been shown to increase leaf area size. The higher concentration of gibberellin leads to the suppression of DELLA proteins in the plant, which are proteins that suppress growth. The expansion in leaf size can lead to greater photosynthetic abilities which increases the plants fitness. Since suppression of DELLA proteins is caused by an increased influx of gibberellin, this too can signify overall increased growth in the plant.

Galls
Galls are abnormal growths on leaves and branches of plants caused by bacteria and fungi. These abnormal growths can cause plant development to be stunted due to the fact that the galls damage the plants nutrient circulatory system. Galls can also cause abnormal photosynthesis, leading to a decrease in the plants fitness.Some Galls are edible and consumed by certain cultures. Galls also can inhibit seed production and inflorescence. Fungi cause galls in plants by significantly increasing auxin in cells causing hypertrophy. Fungi increase auxin levels by producing tryptophan and converting it to auxin. The auxin is then given to the plant to induce continuous transport to certain plant cells. Those cells become abnormally enlarged and galls are produced.

Bakanae
Bakanae also known as foolish seedling disease is caused by the the fungus Fusarium fujikuroi. A seedling that has been infected with bakanae will appear as an elongated, slender chlorotic plant with reduced seed germination. Seedlings can also appear stunted and with foot rot. The mechanism by which this fungus induces such changes in the seedling is through the production of gibberellic acid and fusaric acid. When the fungus provides a surplus of gibberellic acid it causes hypertrophy in the plant inducing hyper-elongation of the plant. The hyper-elongation causes the plant to wither. The surplus of fusaric acid induces stunted growth in seedlings. Stunted growth causes rotting in the root of the plant inducing death. Bakanae is one of the most damaging disease known to rice plants.