Appressorium vs. Haustorium

Attribute	Appressorium	Haustorium
Definition	An infection structure formed by certain fungi to penetrate the host's surface	A specialized structure formed by parasitic plants to extract nutrients from the host
Formation	Develops from germ tubes or hyphae	Develops from modified root or stem cells
Function	Facilitates host penetration and nutrient uptake	Allows parasitic plants to extract nutrients from the host
Location	Usually found on the surface of the host	Penetrates the host's tissues
Structure	Typically finger-like or bulbous structure	Can be branched or unbranched, depending on the species
Host Interaction	Invades the host and establishes a feeding relationship	Forms a connection with the host's vascular system

Introduction

Fungi are fascinating organisms that have evolved various mechanisms to interact with their hosts. Two important structures involved in this interaction are the appressorium and haustorium. Appressorium and haustorium are specialized structures formed by certain fungi during their infection process. While both structures play crucial roles in the establishment of fungal infections, they differ in their morphology, function, and the types of organisms they interact with. In this article, we will explore the attributes of appressorium and haustorium in detail.

Appressorium

Appressorium is a specialized infection structure formed by certain plant pathogenic fungi. It is typically a dome-shaped or flattened structure that develops at the tip of a germ tube or hypha. The appressorium is characterized by its thick, melanized cell wall, which provides mechanical strength and resistance to host defenses. This structure is primarily involved in the penetration of the host surface.

Appressoria are commonly formed by fungi belonging to the order Erysiphales, such as powdery mildews, and the genus Magnaporthe, which causes rice blast disease. These fungi rely on the appressorium to generate enormous turgor pressure, which allows them to mechanically breach the host cuticle or epidermis. The appressorium exerts pressure on the host surface, leading to the formation of a penetration peg that facilitates the entry of the fungus into the host tissues.

Appressoria are typically formed in response to specific environmental cues, such as the presence of hydrophobic surfaces or chemical signals from the host. Once the appressorium has successfully penetrated the host, it differentiates into other specialized structures, such as the haustorium, to establish a nutrient exchange interface with the host.

Haustorium

Haustorium is another specialized structure formed by various parasitic fungi during their infection process. Unlike the appressorium, which is primarily involved in host penetration, the haustorium is responsible for establishing a nutrient exchange interface between the fungus and its host. Haustoria are typically formed by fungi belonging to the order Erysiphales, rusts, and smuts.

The haustorium is a highly specialized structure that develops inside the host cells. It is characterized by its intimate association with the host cytoplasm and the formation of specialized feeding structures, such as haustorial mother cells and haustorial branches. These structures facilitate the uptake of nutrients from the host and the secretion of effector molecules that manipulate host defenses.

Haustoria are formed after the initial penetration of the host by the appressorium or other infection structures. Once inside the host, the fungus establishes a haustorial complex, which allows it to extract nutrients from the host cells. The haustorium also plays a crucial role in suppressing host immune responses, enabling the fungus to establish a successful infection.

Comparison

While both appressorium and haustorium are specialized structures involved in fungal infection, they differ in several aspects:

Morphology

Appressoria are typically dome-shaped or flattened structures that develop at the tip of a germ tube or hypha. They have a thick, melanized cell wall that provides mechanical strength. In contrast, haustoria are highly specialized structures that develop inside the host cells. They form intimate associations with the host cytoplasm and often exhibit branching structures.

Function

The primary function of the appressorium is to penetrate the host surface. It generates turgor pressure to mechanically breach the host cuticle or epidermis. Once inside the host, the appressorium differentiates into other structures involved in nutrient uptake and infection establishment. On the other hand, the haustorium is responsible for establishing a nutrient exchange interface with the host. It facilitates the uptake of nutrients from the host cells and the secretion of effector molecules that manipulate host defenses.

Organisms Interacted With

Appressoria are commonly formed by plant pathogenic fungi, such as powdery mildews and Magnaporthe. They primarily interact with plant hosts and are involved in causing diseases in crops. Haustoria, on the other hand, are formed by various parasitic fungi, including rusts and smuts. They interact with a wide range of hosts, including plants, algae, and even other fungi.

Formation and Environmental Cues

Appressoria are typically formed in response to specific environmental cues, such as hydrophobic surfaces or chemical signals from the host. These cues trigger the differentiation of the appressorium from a germ tube or hypha. Haustoria, on the other hand, are formed after the initial penetration of the host by the appressorium or other infection structures. They develop inside the host cells as the fungus establishes a nutrient exchange interface.

Role in Infection

Appressoria play a crucial role in the initial stages of infection by facilitating host penetration. They generate turgor pressure to breach the host surface and establish a foothold inside the host tissues. Haustoria, on the other hand, are involved in the establishment of a successful infection by facilitating nutrient uptake, manipulating host defenses, and suppressing immune responses.

Conclusion

Appressorium and haustorium are two specialized structures formed by certain fungi during their infection process. While appressoria are primarily involved in host penetration, haustoria establish a nutrient exchange interface with the host. These structures differ in their morphology, function, organisms they interact with, formation cues, and roles in infection. Understanding the attributes of appressorium and haustorium is crucial for unraveling the complex interactions between fungi and their hosts, and for developing strategies to control fungal diseases.