Minisymposium 27: Temperature

Abs # 48004: An Arabidopsis homeodomain transcript factor gene, HOS9 mediates cold tolerance through a novel pathway

Presenter:	Zhu, Jianhua , jhzhu@purdue.edu
Authors	Zhu, Jianhua  (A)   Shi, Huazhong  (A)   Lee, Byeong-ha  (B)   Damsz, Barbara  (A)   Cheng, Shie  (A)   Stirm, Vicki  (A)   Zhu, Jian-Kang  (B)   Hasegawa, Paul M (A)   Bressan, Ray A (A)
Affiliations:	(A): Department of Horticulture and Landscape Architecture, Purdue University (B): Department of Plant Sciences, University of Arizona

To investigate essential components mediating stress signaling in plants, we initiated a large scale stress response screen using Arabidopsis plants carrying the firefly luciferase reporter gene under the control of the stress-responsive RD29A promoter. The RD29A gene can be induced by exposure of plants to low temperature, abscisic acid (ABA) or osmotic stress. Using this screen more than forty mutants were recovered that display altered expression of the RD29A::LUC reporter gene. Here we report the identification and characterization of one of these mutants, hos9-1 (for high expression of osmotically responsive genes) in which the reporter construct was hyperactivated by low temperature, but not by ABA or salinity stress. The mutants grow more slowly and flower later than do wild type plants. They also are more sensitive to freezing than wild type plants both before and after cold acclimation. The HOS9 gene encodes a putative homeodomain transcription factor that is localized to the nucleus. HOS9 is constitutively expressed and is not further induced by cold stress. Cold treatment increased the level of transcripts of several stress-responsive genes, to a higher level in hos9-1 than in wild type plants. However, the CBF/DREB1 (CRT binding factor/DRE binding factor 1) transcription factor genes that mediate a part of cold acclimation in Arabidopsis did not have their response to cold altered by the hos9-1 mutation. Microarray analyses showed that none of the genes affected by the hos9-1 mutation are known to be controlled by the CBF/DREB1 family. Together, these results suggest that HOS9 is important for plant growth and development, and for a part of freezing tolerance, by affecting the activity of genes independent of the CBF pathway.