Studies On Physiological Response To Powdery Mildew Infection And Analysis Of Related Resistance Genes Expression In Hevea Brasiliensis

Powdery mildew is one of the main leaf disease of rubber tree (Hevea brasiliensis), which serious harm to rubber plantation industry in China. Powdery mildew can be controlled by chemical agents, but powdery mildew infection mechanism and resistance mechanism of rubber tree are still unknown, which results in:on one hand, causes powdery mildew fungi developing resistance to the chemical agents, and on the other hand, hinders breeding of rubber tree clones with powdery mildew resistance. Mlo and SGT1are broad spectrum powdery mildew resistance genes, which regulates a variety of plant resistance to powdery mildew. In a variety of monocotyledonous and dicotyledonous plants, such as barley, Arabidopsis proved their resistance to powdery mildew, but little is known about their functions in rubber tree. In this research, plant physiology, bioinformatics, and molecular biology related technologies were used to studying physiological mechanism of rubber tree in response to powdery mildew infection; identifying Mlo and SGT1gene family in the genomes of castor (Riciuns communis L.) and cassava (Manihot esculenta Crantz) which are relatives to rubber tree; identifying and cloning Hevea Mlo and SGT1family members (HbMlo, HbSGT1) using rubber tree transcriptome database; analyzing HbMlo and HbSGTl expressions under powdery mildew infection, plant hormone and stresses treatments by Q-PCR in rubber tree; characterizing the structure and biological function of powdery mildew resistance-related HbMlo and HbSGTl gene. The results are as follows:1. Rubber tree clone CATAS7-33-97were used to studying physiological indices changes of rubber tree in response to powdery mildew infection. The result revealed that powdery mildew infection firstly caused mitochondria damage, and than damaged chloroplast. Moreover, powdery mildew infection increased the levels of reactive oxygen species in the leaves, damaged mitochondria membrane, and decreased photo synthetic activity, eventually leaded to leaves dead.2. Four Hevea Mlo genes (HbMlo) has been identified and cloned, namely HbMlol, HbMlo8, HbMlo9, and HbMlol2. These4HbMlos showed highly homologous to Mlo from other species, containing specific Mlo domain and7-9transmembrane domains, respectively. HbMlo9contained an N-terminal signal peptide.3. Expression analysis revealed that HbMlol, HbMlo8, HbMlo9, and HbMlo12differentially expressed in the bark, latex, flowers and leaves, respectively. Expressions of HbMlol and HbMlo12showed the highest expression level in leaves, while HbMlo8and HbMlo9showed the highest expression level in bark. HbMlo8expression was significantly increased during powdery mildew infection, but HbMlo12expression was decreased during powdery mildew infection, expressions of HbMlol and HbMlo9were not affected by powdery mildew. Expressions of the4genes were induced by drought, wounding, ethephon, abscisic acid, and jasmonic acid treatments, respectively.4. Two Hevea SGT1genes (HbSGT1) has been identified and cloned, namely HbSGTla and HbSGTlb. These2HbSGT1showed highly homologous to SGT1from other species, containing specific TRR repeat sequence, CS and SGS domain. They do no thave transmembrane domains and signal peptide.5. Expression analysis revealed that HbSGT1a, and HbSGT1b differentially expressed in the bark, latex, flowers and leaves, respectively. Expressions of HbSGT1a showed the highest expression level in leaves, however HbSGT1b showed the highest expression level in flower. HbSGT1a and HbSGT1b expression were significantly increased and decreased during powdery mildew infection. Expressions of the2genes were induced by drought, stress hormones and wounding treatments, respectively.According to the above results, we draw the following conclusions:1) Powdery mildew infection lead to continuous leaf damage in rubber tree, which damage to mitochondria earlier and heavier than those to chloroplast;2) HbMlo8and HbMlo12involved in resistance to powdery mildew in Hevea brasiliensis. HbMlol and HbMlo9did not respond to powdery mildew infection, but they associated with wounding and drought stress response;3) HbSGT1a and HbSGT1b involved in resistance to powdery mildew, and wounding, drought and other stress conditions in Hevea brasiliensis.These results will provide a foundation for disease resistance in rubber tree and provide gene resouse in breeding rubber tree clones for disease resistance.