In this study, a phosducin-like protein,PoPlp1, was identified and functionally studied in the cellulase-producing strainPenicillium oxalicum114-2.PoPlp1 was proven to participate in several biological processes, including mycelium development, conidiation, and expression of cellulases and amylases. With deletion ofPoplp1, morphology and development varied significantly in ΔPoplp1. Colony growth, glucose utilization, and the hydrolysis capability of starch and cellulose were limited, whereas conidiation was enhanced. Based on detection of the levels of expression of transcription factors involved in asexual development, we conjectured thatPoPlp1 is involved in conidiation via the major factor BrlA. We explored the effect ofPoPlp1 on cellulase and amylase expression and observed that cellulase and amylase activity and major gene transcription levels were all dramatically reduced in ΔPoplp1. Deletion ofPoPlp1 caused a decrease in intracellular cAMP levels, and the cellulase gene expression level of ΔPoplp1was restored to a certain extent through external addition of cAMP. These findings demonstrate thatPoPlp1 may affect cellulase and amylase expression by regulating cAMP concentration. To comprehensively explore the mechanism ofPoPlp1 in regulating multiple biological processes, we performed a comparative transcriptomic analysis between strainsP. oxalicum114-2 and ΔPoplp1. The major cellulase and amylase genes were all downregulated, congrent with the results of real-time quantitative polymerase chain reaction analysis. The genes involved in the G protein–cAMP signaling pathway, including several G-protein-coupled receptors, one regulator of G protein signaling, and two cAMP phosphodiesterases, were disrupted by deletion ofPoPlp1. These results confirm the positive function ofPoPlp1 in the G protein–cAMP signaling pathway. This functional analysis ofPoPlp1 will be very beneficial for further study of the regulatory mechanisms of cellulase expression and other biological processes inP. oxalicum114-2 via the G protein–cAMP signaling pathway.