Hypobranching Induced by Both Environmental Antioxidants and Ros Metabolism Gene Knockouts in Neurospora Crassa

Abstract

Previous work suggested a role of reactive oxygen species (ROS) metabolism on branch density,
the statistical distribution of physical distances between branch points along a growing hypha in Neurospora.
Here we report the results of experiments designed to ask more generally about the relationship between ROS
and branch density by examining the branching effects of selected ROS metabolism gene knockout mutants
as well as the impact on branching of exogenously added antioxidants. In all ROS metabolism mutants
tested, growth was shown to branch less densely (hypobranching) when grown at lower temperatures, a shift
not observed in the wild-type. Interestingly, this holds true for knockouts of genes expected to reduce ROS as
well as those expected to produce them. In addition, in tests on wild type Neurospora, added ascorbic acid
produced unusual branching patterns. Hypha exposed to exogenous antioxidants display dose dependent
hypobranching with hypha becoming more hypobranched as doses increase. At higher doses, however, the
branch distribution becomes bimodal with one maximum continuing to shift toward hypobranching and the
second maximum representing a spike of very closely spaced branch points.