Transcriptional repression by Oshox1, a novel homeodomain leucine zipper protein from rice

Abstract

This paper describes the characterization of Oshox1, a cDNA clone from rice encoding a member of the homeodomain-leucine zipper (HD-Zip) class of putative transcription factors. Oshox1 maps to chromosome 10 and belongs to a family of related rice genes. Two-hybrid assays showed that Oshox1 protein can homodimerize, but can also form heterodimers with an Arabidopsis HD-Zip protein. This suggests that protein-protein interactions may also occur between different HD-Zip proteins in rice, which would provide enormous versatility for generating specific gene-control mechanisms. Oshox1 mRNA could be detected in various rice tissues at different developmental stages, with highest levels in embryos, shoots of seedlings, and leaves of mature plants. Transgenic expression of Oshox1 in Arabidopsis retarded growth and affected leaf size and shape, indicative of a role as developmental regulator. In vitro and in vivo DNA-binding studies revealed that Oshox1 interacts with the pseudopalindromic sequence CAAT(C/G)ATTG, confirming that the protein represents a transcription factor. Oshox1 was found to repress reporter gene activity in rice suspension cells, most likely by a mechanism of active transcriptional repression. Repression was strictly dependent on the presence of upstream Oshox1 binding sites in the reporter gene constructs and a function of the N-terminal region of Oshox1, preceding the homeodomain.

Different subcellular localization and trafficking properties of KNOX class 1 homeodomain proteins from rice

“…Nuclear localization of the GFP-tagged proteins was confirmed by overlapping signal with a nucleic acid stain (DAPI). N-terminally GFP-tagged rice Oshox1 (Meijer et al, 1997), a different type of homeodomain protein, was used for comparison. In contrast to the partial nuclear localization pattern of the GFP-tagged KNOX proteins, GFP-tagged Oshox1 protein localized exclusively to the nucleus (n ¼ 286, Figure 1E).…”

A Homeodomain Leucine Zipper Gene from Craterostigma plantagineum Regulates Abscisic Acid Responsive Gene Expression and Physiological Responses

“…In vitro and in vivo binding assays have demonstrated that HDZip proteins from Arabidopsis, C. plantagineum and rice preferentially bind to two 9-bp pseudopalindromic sequences, CAA-T(A/T)ATTG (HDE1) and CAAT(G/C)ATTG (HDE2) (Frank et al, 1998;Meijer et al, 2000;Johannesson et al, 2001;Deng et al, 2002). Furthermore, different HDZip factors were shown to act either as repressors or as activators of HDEcontaining synthetic reporter genes (Meijer et al 1997;Ohgishi et al 2001). Autoregulation through HDE sites in their own promoters was demonstrated for the Arabidopsis HDZips, ATHB2 and ATHB6 (Ohgishi et al, 2001;Himmelbach et al, 2002).…”

Isolation and characterization of two homeodomain leucine zipper genes from the dioecious plant Silene latifolia.

“…These signal transduction networks are related to the general growth regulation of plants. The overexpression of sense or antisense HD-Zip I or II mRNA usually alters the growth rate and development of a plant (Schena et al, 1993;Aoyama et al, 1995;Meijer et al, 1997). Most members of the HD-Zip III subfamily play roles in cell differentiation in the stele (Baima et al, 1995;Zhong and Ye, 1999).…”