Cloning and characterization of an HDZip I gene GmHZ1 from soybean

By using cDNA-AFLP, we analyzed a recombinant inbred line population of soybean that was derived from a soybean mosaic virus (SMV) resistant cultivar Kefeng No.1 and a susceptible cultivar Nannong 1138-2. One hundred and eight fragments showing polymorphism between SMV resistant and susceptible pools were identified. One fragment w27 was 96 bp in length and showed homology to homeobox ggth with a coding region of 738 bp, encoding a protein of 245 amino acids. The genomic sequence analysis defined an intron of 521 bp in the coding region. GmHZ1 was characterized by the presence of a homeodomain (HD) with a closely linked leucine zipper motif (Zip). Southern blot analysis indicated that there was a single copy of GmHZ1 in the soybean genome. When inoculated with SMV strain N3, resistant and susceptible varieties showed reduced and increased expression of the GmHZ1, respectively. The fusion protein of GmHZ1 with GFP was targeted only in nucleus. Yeast two hybrid studies revealed that the GmHZ1 had transcriptional activation activity and can form homodimer. GmHZ1 can bind two 9-bp pseudopalindromic elements (CAAT(A/T)ATTG and CAAT(C/G)ATTG) with different affinity. Using GUS as a reporter gene, GmHZ1 was proved to be a transcriptional activator and enhanced GUS expression by binding with the two elements in plant cells. These results indicate that the GmHZ1 may have a transcriptional activator function in plant response to SMV infection.