Harpins are bacterial proteins that can enhance plant growth and defense against pathogens and insects. To elaborate whether harpins perform the diverse functions in coordination with the activation of specific promoters that contain particular elements, we cloned pathogen-inducible plant promoters PPP1, PPP2, and PPP3 from tobacco and investigated their responses to harpinxoo or its truncated fragments DEG, DIR, and DPR (domains for enhancing plant growth, insect resistance and pathogen resistance). PPP1 contains an internal repeat composed of two tandem 111bp fragments; 111bp in the repeat was deleted in PPP2. PPP3 contains a bacteria-inducible element; PPP1 and PPP2 additionally contain TAC-1 and Eli boxes inducible correspondingly by salicylic acid (SA) and elicitors. Function of cloned PPPs was confirmed based on their activation in transgenic Arabidopsis plants by Ralstonia solanacearum (Ralston) or SA. Harpinxoo, DEG, DIR, or DPR activated PPP1 and PPP2 but not PPP3, consistent with the presence of Eli boxes in promoters. PPP1 was ca. 3-fold more active than PPP2, suggesting that the internal repeat affects levels of the promoter activation.
Three hrfA (hypersensitive response-functioning faction A) homologues (hrf1, hrf2 and hrf3) are cloned from 12 strains of Xanthomonas oryzae using PCR based techniques. Hrf1, hrf2 and hrf3 are derived from strains belonging to X. o. pv. oryzae, X. o. pv. oryzicola and X. o. pv. oryzae respectively. Sequence analysis shows that all three genes encode glycine-rich pro-teins with various numbers of GGG-GG motifs. They all share a conserved cysteine residue at position 45 or 47. Hrf1 and hrf3 encode HarpinXoo while hrf2 encodes Harpinxooc. Hrf1 and hrf3 encodes two different types of HarpinXoo proteins. Hrf1 from X. o. pv. oryzae strains ( JxoIII, JxoIV, Jxov, Pxo61, Pxo76, Pxo79, Pxo99, Pxo99 and Pxo124) encodes a 15.6 kD HarpinXoo with 3 GGG-GG motifs while Hrf3 from strain Pxo86 and Pxo112 encodes a 15.9 kD Harpinxoo with 4 GGG-GG motifs. Harpinxooc encoded by hrf2 from X. o. pv. oryzicola (strain RS105) has the mo-lecular weight of 15.3 kD and contains 2 GGG-GG motifs. Cluster analysis is performed using deduced sequences of hrf1, hrf2 and hrf3 as well as previously reported Hpa1 and XopI protein sequence. The results indicated that Harpinxoo and Harpinxooc belong to two closely related sub-groups. Hrf, hrf2 and hrf3 are expressed in E. coli strain BL21 successfully. Under the same condition, hrf1, hrf2 and hrf3 are expressed at the level of 0.389, 0.530 and 0.083 mg/mL re-spectively. All expressed hrf1, hrf2 and hrf3 proteins (Harpins) are shown to be able to induce hypersensitive reaction and TMV resistance on tobacco. Among the three proteins, Hrf2 has the highest activity while Hrf3 has the lowest activity.
LI Ping, LU Xuzhong, SHAO Min, LONG Juying & WANG Jinsheng Department of Plant Pathology, Nanjing Agricultural University
采用H2O2和酶活性检测、DAB染色、定量实时PCR等方法研究转hpa1Xoo基因棉花T-34叶组织中的活性氧。结果显示:无病原菌侵染时,T-34和出发品种Z35均未产生活性氧。在接种黄萎病菌分生孢子悬浮液后,与Z35相比,在T-34叶组织中接菌0～8 h H2O2含量变化呈现2个峰值;接菌8 h时PAL和POD酶活性显著增强;DAB染色显示褐红色斑产生;2个防卫基因ghAOX1和hsr203J超表达。这些结果表明,转hpa1Xoo基因棉花为某些防卫基因超水平表达提供了分子基础,使受到病原菌侵染时才诱导产生的高水平活性氧及相关基因表达,并且组成型表达的HarpinXoo赋予转基因棉花对黄萎病菌的抗性。
