Present address: Department of Applied Biological Sciences, Arizona State University at the Polytechnic Campus, Mesa, AZ 85212, USA.
Identification of the novel protein QQS as a component of the starch metabolic network in Arabidopsis leaves
Article first published online: 19 FEB 2009
© 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd
The Plant Journal
Volume 58, Issue 3, pages 485–498, May 2009
How to Cite
Li, L., Foster, C. M., Gan, Q., Nettleton, D., James, M. G., Myers, A. M. and Wurtele, E. S. (2009), Identification of the novel protein QQS as a component of the starch metabolic network in Arabidopsis leaves. The Plant Journal, 58: 485–498. doi: 10.1111/j.1365-313X.2009.03793.x
- Issue published online: 27 APR 2009
- Article first published online: 19 FEB 2009
- Received 22 September 2008; revised 16 December 2008; accepted 23 December 2008; published online 19 February 2009.
- protein with unknown functions;
- starch regulation;
Little is known about the role of proteins that lack primary sequence homology with any known motifs (proteins with unknown functions, PUFs); these comprise more than 10% of all proteins. This paper offers a generalized experimental strategy for identifying the functions of such proteins, particularly in relation to metabolism. Using this strategy, we have identified a novel regulatory function for Arabidopsis locus At3g30720 (which we term QQS for qua-quine starch). QQS expression, revealed through global mRNA profiling, is up-regulated in an Arabidopsis Atss3 mutant that lacks starch synthase III and has increased leaf starch content. Analysis of public microarray data using MetaOmGraph (metnetdb.org), in combination with transgenic Arabidopsis lines containing QQS promoter–GUS transgenes, indicated that QQS expression responds to a variety of developmental/genetic/environmental perturbations. In addition to the increase in the Atss3 mutant, QQS is up-regulated in the carbohydrate mutants mex1 and sis8. A 586 nt sequence for the QQS mRNA was identified by 5′ and 3′ RACE experiments. The QQS transcript is predicted to encode a protein of 59 amino acids, whose expression was confirmed by immunological Western blot analysis. The QQS gene is recognizable in sequenced Arabidopsis ecotypes, but is not identifiable in any other sequenced species, including the closely related Brassica napus. Transgenic RNA interference lines in which QQS expression is reduced show excess leaf starch content at the end of the illumination phase of a diurnal cycle. Taken together, the data identify QQS as a potential novel regulator of starch biosynthesis.