Cloning And Expression Of Receptor-like Protein Genes Mediating Verticillium Dahliae Resistance And A Mannose-binding Lectin Gene From Plants

Caused by Verticillium pathogens such as V. dahliae etc., verticillium wilt is a worldwide disastrous plant vascular disease infecting many important crops such as cotton, eggplant, tomato, potato and clover etc. with heavy yield loss. As a soil-born disease, it has a very broad host range. Chemical control of this disease is of high cost and less efficient accompanied with food safety and environment safety problems. Selecting verticillium resistant cultivars is the basic strategy to control this disease, but it is confined by long term of selection and deficiency of resistance genotypes. Gene engineering is an adequate strategy to create new breeding germplasms by isolating and transforming useful verticillium resistance-related genes with short term and without confinement from reproductive barriers.According to Gene-for-gene Theory, the core mechanism of plant resistance to pathogen invasion lies in the primary recognition between the receptor-like protein of the resistance gene (R) product of the host and me ligand (or elicitor) of the avirulence gene (Avr) product of the pathogen. Many resistant and susceptible plant genotypes are not typically differed in downstream defensive genes but in whether or not possessing an adequate resistance gene and in the mechanism of defense-related signal transduction. To date 6 types of plant resistance genes have been cloned, most of which conform to Gene-for-gene Theory and encode cytoplasmic or transmembrane receptor-like proteins which can mediate signal transduction related to disease resistance. Expression of these R genes in susceptible plants resulted in acceptable enhancement of disease resistance.Besides R-Avr recognition, more and more evidences indicate that the PG-PG1P recognition on the plant cell wall can also mediate systemic defense reactions. A primary pathogenetic strategy of fungal pathogens is to secrete hydrolytic enzymes, the most primary of which is polygalacturonase (PG), to destruct the plant cell wall. On the other hand, the plant kingdom also evolves a molecular arm which is called polygalacturonase-inhibiting protein (PGIP) to restrict the activity of PG PGIP can specifically, reversibly andsaturably bind to PG and prevent or delay the degradation of the cell wall ingredient polygalacturonic acid, which increases the concentration and prolongs the half life of the oligogalacruronide (OGA). OGA with a certain DP (degree of polymerization) is a kind of elicitor-active oligosaccharin, which enters the cell and is recognized by the membrane-associated oligosaccharin receptor and thus certain defensive signaling pathways are activated to induce the transcriptional expression of phytoaiexin synthesis enzymes, proteinase inhibitors (Pis), pathogenesis-related proteins (PRs) and other defensive-related proteins. PGIP as well as the plant R proteins are all members of the LRR (leucine-rich repeat) type receptor-like glycoprotein superfamily, which recognize foreign molecules and mediate defensive reactions. The variable amino acid residues flanking the conserved leucine residues within the strand/ turn motif of the LRR unit is characterized as the determinant factor of recognition specificity. Single residue mutations of them are enough to change the specificity.Verticillium resistance engineering on most plant species such as cotton has poorly yielded, but a striking advancement has been achieved on tomato. By using map-based cloning method, the family members Ve\ and Vel of verticillium wilt resistance gene locus have been isolated from tomato (Lycopersicon esculentwn Mill.). One extinct feature of them is mat they are not typically race-specific, e.g., transformation of them into potato can enhance resistance to V. albo-atrum. But these 2 genes are not resistant to V. dahlias race 2, so it is still uigent to seek new genes to suppress this highly toxic race. Some relative species of tomato from family Solanaceae such as the wild eggplant species Solomon torvum shows almost immunity to Verticillium wilt and other diseases. Because...