The Function Analysis Of Potassium In Rice Resistance To Meloidogyne Graminicola

The occurrence area of Meloidogyne graminicola（hereinafter referred to as root-knot nematode（RKN））has been increasing year by year in rice planting areas in southern China,which seriously threatens the safety of rice production.Potassium（K）,an important nutrient element,enhances plant tolerance agnisit biotic and abiotic stress.Potassium fertilizer application can effectively reduce the occurrence of plant disease and increase crop yield.However,the founction of potassium in rice defence against RKN are unknown.Potassium channels and transporters systems play an important role in plant resistance to abiotic stress,but there are few studies on the resistance to biotic stresses.We evaluated the resistance induced by K₂SO₄ to RKN in rice and further explored the mechanism of K₂SO₄-induced resistance,and then preliminary studied the role and function of potassium channels and transporters systems in the process of resistance to RKN in rice.The main results are as follows:1.K₂SO₄ treatment decreased the infection and development level of RKNs,and effectively improved the resistance of rice against RKNs.At 14 dpi,the numbers of both root galls and nematodes in rice treated with 0.5 m M K₂SO₄ decreased by 57.2±4.4% and 59.2±6.6%,respectively.The proportion of adult females（70.9±5.6%） was significantly lower than that of control（90.7±5.1%）,while the proportion of juveniles（J3 + J4）（27.0±6.3%） was significantly higher than that of control（6.0±3.2%）.2.K₂SO₄-induced resistance was not achieved by affecting the attraction of rice roots to RKNs and the development of giant cells at the feeding sites of RKNs.Compared with water treatment,there was no significant difference in the number of RKNs attracted around the root tip of rice treated with K₂SO₄ at 10 hpi,and there was no significant difference in the morphology,size and number of giant cells at the feeding sites of RKNs in the root galls of rice treated with K₂SO₄ at 7 dpi.3.K₂SO₄ treatment enhanced callose deposition and rapidly stimulated the accumulation of hydrogen peroxide（H₂O₂）,which initiated the basic defense of rice against nematodes.At 7 dpi,the callose deposit area in root galls of rice treated with K₂SO₄ increased by 67.9%.At 8 and 24 hpi,the content of H₂O₂ in rice roots treated with K₂SO₄ increased by 78.2% and 118.7%,respectively.4.K₂SO₄ treatment up-regulated the expression of disease-resistance related genes in rice.At the early stage of RKNs infection,the expression levels of JA / ET /BR signaling pathway related genes and pathogenesis-related（PR）genes OsPR1 a and OsPR1 b in rice were significantly higher in the K₂SO₄ treated group than untreated.5.Potassium channel OsAKT1 and transporter Os SHAK5 not only play independent roles in rice resistance against RKNs,but also participate in the K₂SO₄-induced resistance mechanism.The number of both root galls and nematodes in the two gene-deficient plants were higher than those in the wild-type plants regardless of the treatment with or without K₂SO₄,and the K₂SO₄-induced resistance in the two genotypic plants was weaker than that in the wild-type plants.6.The potassium transporter Os HAKP is located on the cell membrane and interacts with nematode protein Mg HIP on the cell membrane;the deletion of Os HAKP will increase the susceptibility of rice to RKNs,while overexpression of this gene will increase the resistance of rice,and its developmental expression period corresponds to the developmental expression period of Mg HIP.