Function And Mechanism Of The Cell-wall Invertase GIF1in Regulating Disease Resistance In Rice (Oryza Sativa L.)

Sucrose as an important energy and signaling molecules in plants must be cleavage into hexoses before using. This process is regulated by synthase (Sucrose synthase, SuSy) and invertase enzyme (Invertase, Inv). In contrary to the reversible process of sucrose synthase which cleavage sucrose (Sue) into uridine diphosphate glucose and frucose, invertase catalyze the irreversible hydrolysis of sucrose into glucose (Glu) and fructose (Fru), and play a crucial role in building plant organs, sugar transporting, phloe unloading and regulating the sugar composition of sink organs. Cell wall invertase (cw-Inv) plays a crucial role in plant development and many stresses. There have many findings demonstrating that cell wall invertase can be induced by abiotic and biotic stress and further induce plant defense responses. In this study, we verified that GIF1/OsCIN2can be induced by bacterial blight {Xanthomonas oryzae pv oryzae, Xoo) and fungal blast(Magnaporthe oryzae, M. oryzae) and the GIF1/OsCIN2transgenic plants showed strongly increased resistance to these two pathogens.When infected with pathogen, plant cell wall is the first barrier for pathogen infection, meanwhile plant also monitoring the cell wall integrity and quickly activate defense pathway to minimize pathogen invasion and reduce disease spread. The mutant gifl (grain incomplete filling) was susceptive to postharvest pathogenic fungi (Rhizopus sp.; Alternaria sp.), microarray data and RT-PCR results showed that cell wall synthesis genes were greatly regulated in the gifl mutant. In addition, we also found that the cell wall thickness in mutant become thinner compared to wild type plants and this might be one reason in hypersusceptibel pathogens. On this basis, we generated transgenic plants to investigate the resistant function of GIF1/OsCIN2. The results showed that the cell wall obiviously become thicker in GIF1/OsCIN2transgenic plants than that in wild type plants after pathogen invasion. In addition, cellulose is a crucial composition of plant cell wall, chemical effects as well as genetic regulation that affect cellulose biosynthesis and content confer plants with enhanced resistance against pathogens. Consistently, we found that the cellulose content increased highly in GIF1/OsCIN2trangenic plants. This change also plays an important role in enhancing plant resistance. Besides cellulose, xylose (xyl) is another important factor in plant cell wall defense responses, the results shown that the content of xylose in transgenic plants was increased significantly.Apart from physical defense mechanism, when pathogens infect plants, there have material format in the infection sites, such as the deposition of callose, the formation of CWAs (cell wall positions, CWAs; papillae) and inductin of H2O2and so on. When infected by Xoo and M. oryzae, there was higher level deposition of callose in GIF1/OsCIN2transgenic plants than that in wild type plants. On the other hand, there were many autophyage bodies in the infected cells and there was the formation of CWAs in M. oryzae infection. Meanwhile, we also found that there was accumulation of H2O2and further activated PCD (Programmed Cell Death, PCD).Plant defense responses need much more sugar as energy and the nutritional banlance of sugar in plants have an important role in plant against external biotic stresses. When plants infect with pathogens, there have a transition of source and sink in infected sites, induction of defense genes and photosynthetic genes suppression, this conversion can further stimulate plant defense responses.The mutant gifl was susceptive to postharvest pathogenic fungi, the results shown that the muant gifl in vivo sugar transport han been damaged, the contens of sucrose, glucose and futcose reduced highly and this might result in mutant cell wall becoming thinner. However, the contents of these three sugars increased in transgenic plants and high sugar signal may also be one of the reasons which stimulating plant defense responses. Consistently, we also verified the expression of defense genes and photosynthesis-related genes and found that defense genes were up regulated significantly and the expression of photosynthesis genes was repressed in transgenic plants.Our results verified that cell wall invertase GIF1/OsCIN2has an important regulation function in physical and induced resistance by influencing sugar metaboliztion pathway. Thus, it is a link between energy metaboliztion and plant defense reponses regulation and give a modle for studying cereal plant resistance function in genetics and biochemistry.