title: Identification and characterization of the glucose dual-affinity transport system inNeurospora crassa: pleiotropic roles in nutrient transport, signaling, and carbon catabolite repression.
abstract: BACKGROUND
  The glucose dual-affinity transport system (low- and high-affinity) is a conserved strategy used by microorganisms to cope with natural fluctuations in nutrient availability in the environment. The glucose-sensing and uptake processes are believed to be tightly associated with cellulase expression regulation in cellulolytic fungi. However, both the identities and functions of the major molecular components of this evolutionarily conserved system in filamentous fungi remain elusive. Here, we systematically identified and characterized the components of the glucose dual-affinity transport system in the model fungusNeurospora crassa.
  
  
  RESULTS
  Using RNA sequencing coupled with functional transport analyses, we assigned GLT-1 (Km= 18.42 ± 3.38 mM) and HGT-1/-2 (Km= 16.13 ± 0.95 and 98.97 ± 22.02 µM) to the low- and high-affinity glucose transport systems, respectively. The high-affinity transportershgt-1/-2complemented a moderate growth defect under high glucose whenglt-1was deleted. Simultaneous deletion ofhgt-1/-2led to extensive derepression of genes for plant cell wall deconstruction in cells grown on cellulose. The suppression by HGT-1/-2 was connected to both carbon catabolite repression (CCR) and the cyclic adenosine monophosphate-protein kinase A pathway. Alteration of a residue conserved across taxa in hexose transporters resulted in a loss of glucose-transporting function, whereas CCR signal transduction was retained, indicating dual functions for HGT-1/-2 as "transceptors."
  
  
  CONCLUSIONS
  In this study, GLT-1 and HGT-1/-2 were identified as the key components of the glucose dual-affinity transport system, which plays diverse roles in glucose transport and carbon metabolism. Given the wide conservation of the glucose dual-affinity transport system across fungal species, the identification of its components and their pleiotropic roles in this study shed important new light on the molecular basis of nutrient transport, signaling, and plant cell wall degradation in fungi.
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 China.|University of Chinese Academy of Sciences, Beijing, 100049 China.|School of Ophthalmology and Optometry, Eye Hospital, State Key Laboratory Cultivation Base and Key Laboratory of Vision Science, Ministry of Health and Zhejiang Provincial Key Laboratory of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, 325027 China.
authors.forename: Bang
authors.initials: B
authors.lastname: Wang
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 China.
authors.forename: Jingen
authors.initials: J
authors.lastname: Li
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 China.|School of Life Sciences, Heilongjiang University, Harbin, 150080 Heilongjiang China.
authors.forename: Jingfang
authors.initials: J
authors.lastname: Gao
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 China.
authors.forename: Pengli
authors.initials: P
authors.lastname: Cai
authors.affiliation: School of Life Sciences, Heilongjiang University, Harbin, 150080 Heilongjiang China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Han
authors.affiliation: Key Laboratory of Systems Microbial Biotechnology, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308 China.
authors.forename: Chaoguang
authors.identifier: 0000-0002-0305-2178
authors.initials: C
authors.lastname: Tian
keywords: Cellulase; Dual-affinity; GLT-1; Glucose transporter; HGT-1/-2; Signaling