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PubMed2005

Induction of wheat defense and stress-related genes in response to Fusarium graminearum.

Fusarium head blight (FHB), caused by species of the fungus Fusarium, is a worldwide disease of wheat (Triticum aestivum L.). The Chinese T. aestivum 'Ning7840' is one of few wheat cultivars with resistance to FHB. To identify differentially expressed genes corresponding to FHB resistance, a cDNA library was constructed using pooled mRNA isolated from glumes of 'Ning7840' harvested at 2, 6, 12, 24, 36, 72, and 96 h after inoculation (hai) with a conidia spore suspension of Fusarium graminearum. Suppressive subtractive hybridization (SSH) cDNA subtraction was carried out using pooled glume mRNAs from the tester and the control. The cDNA library was differentially screened using the forward subtracted cDNAs and the reverse subtracted cDNAs as probes. Twenty-four clones with significant matches to either plant (16 sequences) or fungal (8 sequences) genes were isolated based on their specific hybridization with forward subtracted cDNA and not reverse subtracted cDNA. Six putative defense-related genes were confirmed by real-time quantitative reverse-transcriptase PCR. Many-fold higher induction of three clones (A3F8, B10H1, and B11H3) in the resistant genotypes compared with susceptible genotypes indicates a putative role in the resistance response to Fusarium graminearum. Transcript accumulations of P450, chitinase (Chi1), and one unknown gene (clone B8Q9) in both resistant and susceptible genotypes suggest an involvement in a generalized resistance response to F. graminearum. Nucleotide sequence analysis showed that cDNA clone A4C6 encodes a cytochrome P450 gene (CYP709C3v2), including 14 N-terminal amino acids that have a membrane-associated helical motif. Other domains characteristic of eukaryotic P450 are also present in CYP709C3v2. The deduced polypeptide of cDNA clone B2H2 encodes an acidic isoform of class I chitinase containing a 960-bp coding region. Southern hybridization using aneuploid lines of T. aestivum 'Chinese Spring' indicated that CYP709C3v2 was located on the short arm of chromosomes 2B and 2D.

Amino Acid Sequence↗

PubMed1995

The G protein gamma subunit. Requirements for dimerization with beta subunits.

Guanine nucleotide-binding protein beta and gamma subunits form a tightly bound complex that can only be separated by denaturation. Assembly of beta and gamma subunits is a complicated process. The beta 1 and gamma 2 subunits can be synthesized in vitro in rabbit reticulocyte lysate and then assembled into dimers, but beta 1 cannot form beta gamma dimers when synthesized in a wheat germ extract. In contrast, gamma 2 translated in either system can dimerize with beta 1, suggesting that dimerization-competent gamma 2 can be synthesized without the aid of specific chaperonins or other cofactors. Dimerization-competent gamma 2 in solution forms an asymmetric particle with a Stokes radius of about 21 +/- 0.4 A (n = 4), s20,w of 0.9 S (range 0.8-1.0 S, n = 2), and frictional ratio of 1.57 (assuming no hydration). To define the part of gamma 2 that is needed for native beta gamma dimer formation, a series of N- and C-terminal truncations were generated, synthesized in vitro, and incubated with beta 1. Dimerization was assessed by stabilization of beta 1 to tryptic proteolysis. Truncation of up to 13 amino acids at the C terminus did not affect dimerization with beta 1, whereas removal of 27 amino acids prevented it. Therefore, a region between residues 45 and 59 of gamma 2 is important for dimerization. Truncation of 15 amino acids from the N terminus greatly diminished the formation of beta gamma dimers, while removal of 25 amino acids entirely blocked it. Thus, another region important for forming native beta gamma is near the N terminus. Extension of the N terminus by 12 amino acids that include the influenza virus hemagglutinin epitope did not prevent beta gamma dimerization. Furthermore, in intact 35S-labeled COS cells, epitope-tagged gamma 2 coimmunoprecipitates with beta and alpha subunits. The N-terminal epitope tag must lie at the surface of the heterotrimer since it prevents neither heterotrimer formation nor access of the antibody.

Amino Acid Sequence↗