| Summary: | L-Sorbose induces hyperbranching of hyphae, which results in colonial growth in <i>Neurospora crassa.</i> The <i>sor</i>-4 gene, which encodes a glucose sensor that acts in carbon catabolite repression (CCR), has been identified as a sorbose resistance gene. In this study, we found that the deletion mutant of <i>col</i>-26, which encodes an AmyR-like transcription factor that acts in CCR, displayed sorbose resistance. In contrast, the deletion mutants of other CCR genes, such as a hexokinase (<i>hxk</i>-2), an AMP-activated S/T protein kinase (<i>prk</i>-10), and a transcription factor (<i>cre</i>-1), showed no sorbose resistance. Double mutant analysis revealed that the deletion of <i>hxk</i>-2, <i>prk</i>-10, and <i>cre</i>-1 did not affect the sorbose resistance of the <i>col</i>-26 mutant. Genes for a glucoamylase (<i>gla</i>-1), an invertase (<i>inv</i>), and glucose transporters (<i>glt</i>-1 and <i>hgt</i>-1) were highly expressed in the <i>cre</i>-1 mutant, even in glucose-rich conditions, but this upregulation was suppressed in the Δ<i>cre</i>-1; Δ<i>col</i>-26<i>a</i> double-deletion mutant. Furthermore, we found that a <i>dgr</i>-2(L1)<i>a</i> mutant with a single amino-acid substitution, S11L, in the F-box protein <i>exo</i>-1 displayed sorbose resistance, unlike the deletion mutants of <i>exo</i>-1, suggesting that the function of <i>exo</i>-1 is crucial for the resistance. Our data strongly suggest that CCR directly participates in sorbose resistance, and that <i>col</i>-26 and <i>exo</i>-1 play important roles in regulating the amylase and glucose transporter genes during CCR.
|
|---|