A screen for Neurospora knockout mutants displaying growth rate dependent branch density.

Branch density (the spatial distribution of branch initiation points along a growing hypha) in wild-type Neurospora has been shown to remain constant at different growth rates due to a hypothesized system which compensates for hyphal growth rate. Here we report the results of a survey of the Neurospora knockout library for mutants affecting this proposed growth rate compensation system. The mutants identified fail to maintain branching homeostasis at different growth rates, thus showing growth rate-dependent branch density. The gene functions highlighted by this screen are diverse with several emerging themes including: ubiquitin-binding proteins, kinases, metal binding/metal metabolism proteins, reactive oxygen species (ROS) control proteins, and clock-associated/clock-controlled proteins. Other than their common influence on branch density homeostasis, the relationships between these gene functions and how they interact to influence branching are unclear.