Branching of fungal hyphae: regulation, mechanisms and comparison with other branching systems.

The ability of rapidly growing hyphae to generate new polarity axes that result in the formation of a branch represents one of the most important yet least understood aspects of fungal cell biology. Branching is central to the development of mycelial colonies and also appears to play a key role in fungal interactions with other organisms. This review presents a description of the two major patterns of hyphal branching, apical and lateral, and highlights the roles of internal and external factors in the induction of branch formation. In addition, potential mechanisms underlying branch site selection are outlined, and the possible roles of multiple signaling pathways (i.e., G protein alpha, Cdc42, NDR kinases) and subcellular structures (i.e., the Spitzenkorper, septins) are discussed. Finally, other forms of branching in the plant and animal kingdoms are briefly summarized and compared to hyphal branching.