Functional analysis of rice HOMEOBOX4 (Oshox4) gene reveals a negative function in gibberellin responses.
The homeodomain-leucine zipper (HD-Zip) putative transcription factor genes are divided into 4 families. In this work, we studied the function of a rice HD-Zip I gene, H OME O BO X4 (Oshox4). Oshox4 transcripts were detected in leaf and floral organ primordia but excluded from the shoot apical meristem and the protein was nuclear localized. Over-expression of Oshox4 in rice induced a semi-dwarf phenotype that could not be complemented by applied GA3. The over-expression plants accumulated elevated levels of bioactive GA, while the GA catabolic gene GA2ox3 was upregulated in the transgenic plants. In addition, over-expression of Oshox4 blocked GA-dependent alpha-amylase production. However, down-regulation of Oshox4 in RNAi transgenic plants induced no phenotypic alteration. Interestingly, the expression of YAB1 that is involved in the negative feedback regulation of the GA biosynthesis was upregulated in the Oshox4 over-expressing plants. One-hybrid assays showed that Oshox4 could interact with YAB1 promoter in yeast. In addition, Oshox4 expression was upregulated by GA. These data together suggest that Oshox4 may be involved in the negative regulation of GA signalling and may play a role to fine tune GA responses in rice.
National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China.
Mingqiu
M
Dai
Yongfeng
Y
Hu
Qian
Q
Ma
Yu
Y
Zhao
Dao-Xiu
DX
Zhou
D000595:Amino Acid Sequence; D000681:Amylases / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005875:Gibberellins / Q000378:metabolism / Q000494:pharmacology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D012275:Oryza / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D030821:Plants, Genetically Modified; D011485:Protein Binding; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020798:Two-Hybrid System Techniques
D005875:Gibberellins; D018398:Homeodomain Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D000681:Amylases