| Filamentous fungi play important roles in health care, agriculture, and bioprocessing. In many situations, they experience nutrient starvation. In some cases, nutrient starvation detrimentally affects cellular morphology and physiology; in other cases, it can be beneficial. Thus, a better understanding of how starvation influences morphology may result in strategies to control morphology to our advantage. However, little is known about how individual fungal mycelia respond to nutrient starvation at the cellular and molecular level.;For studies at the cellular level, we grew fungal mycelia in a parallel plate flow chamber, which allows for complete environmental control while monitoring individual mycelia over time. We discovered that the first response to carbon starvation is cessation of growth (i.e. lag time) before mycelia resume re-growth at a lower rate. During this lag time, vacuolation increases significantly, implying significant cellular restructuring and recycling. We propose a model in which the duration of the lag time is determined by the production rate of endogenous carbon and mycelial size.;For studies at the molecular level, we investigated the role of autophagy using a strain of the model fungus Aspergillus nidulans. Autophagy is a non-specific degradation pathway that provides recycled nutrients to sustain growth during nutrient deprivation. Deletion of the putative autophagy gene Anatg13 has significant morphological effects, even during non-starvation conditions, i.e., delayed spore germination, reduced growth and branching rates, and effects on cell wall formation. These data strongly suggest that the putative Atg13 protein is involved in cellular growth and morphological development. Also, we find a lag before re-growth following carbon starvation but not following nitrogen starvation, which suggests that mycelia adapt to nitrogen starvation more rapidly than to carbon starvation. We also treated the Anatg13 deletion mutant with an autophagy-inducing drug, rapamycin, which results in a larger reduction in specific growth rate compared to nitrogen starvation. The specific branching rate of the An atg13 deletion mutant strain was not significantly reduced during nutrient starvation or rapamycin treatment, suggesting a role for Atg13 in branching control. This study is the first to characterize the morphological role of Atg13 in filamentous fungi. |
