J Integr Plant Biol. ›› 2016, Vol. 58 ›› Issue (2): 127-135.DOI: 10.1111/jipb.12366

Special Issue: Rice Genomics and Agriculture

• Metabolism and Biochemistry • Previous Articles     Next Articles

Role of rice cytosolic hexokinase OsHXK7 in sugar signaling and metabolism

Hyun-Bi Kim1†, Jung-Il Cho1†‡, Nayeon Ryoo1‡§, Dong-Ho Shin2, Youn-Il Park2, Yong-sic Hwang3, Sang-Kyu Lee1, Gynheung An1 and Jong-Seong Jeon1*   

  1. 1Crop Biotech Institute & Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, Korea
    2Department of Biology, Chungnam National University, Daejeon 305-764, Korea
    3Department of Bioscience and Biotechnology, Konkuk University, Seoul 143-701, Korea
  • Received:2015-01-23 Accepted:2015-05-03 Published:2015-05-07
  • About author:These authors contributed equally to this work.
    Present address: National Academy of Agricultural Science, Rural Development Administration, Suwon 441-853, Korea.
    §Present address: Center for Neuroscience, Korea Institute of Science and Technology, Seoul 139-791, Korea.
    *Correspondence: E-mail: jjeon@khu.ac.kr

Abstract:

We characterized the function of the rice cytosolic hexokinase OsHXK7 (Oryza sativa Hexokinase7), which is highly upregulated when seeds germinate under O2-deficient conditions. According to transient expression assays that used the promoter:luciferase fusion construct, OsHXK7 enhanced the glucose (Glc)-dependent repression of a rice α-amylase gene (RAmy3D) in the mesophyll protoplasts of maize, but its catalytically inactive mutant alleles did not. Consistently, the expression of OsHXK7, but not its catalytically inactive alleles, complemented the Arabidopsis glucose insensitive2-1 (gin2-1) mutant, thereby resulting in the wild type characteristics of Glc-dependent repression, seedling development, and plant growth. Interestingly, OsHXK7-mediated Glc-dependent repression was abolished in the O2-deficient mesophyll protoplasts of maize. This result provides compelling evidence that OsHXK7 functions in sugar signaling via a glycolysis-dependent manner under normal conditions, but its signaling role is suppressed when O2 is deficient. The germination of two null OsHXK7 mutants, oshxk7-1 and oshxk7-2, was affected by O2 deficiency, but overexpression enhanced germination in rice. This result suggests the distinct role that OsHXK7 plays in sugar metabolism and efficient germination by enforcing glycolysis-mediated fermentation in O2-deficient rice.

 

Kim HB, Cho JI, Ryoo N, Shin DH, Park YI, Hwang Ys, Lee SK, An G, Jeon JS (2016) Role of rice cytosolic hexokinase OsHXK7 in sugar signaling and metabolism. J Integr Plant Biol 58: 127–135 doi: 10.1111/jipb.12366

Key words: Germination, metabolism, OsHXK7, O2 deficiency, rice, signaling, sugar

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