Identification Of The Alternate Hosts Of Puccinia Striiformis F.sp.Tritici(Pst) And Analysis Of The Expression Pattern Of Barberry NPR1 Gene During The Pst Infection.

Wheat stripe rust(yellow rust),caused by Puccinia striiformis f.sp.tritici(Pst)has been a biological disasters threatening the safety of wheat production in China.Growing resistant wheat cultivars is an important approach for the control of the disease.Studies have demonstrated that emergence of new Pst races is the main reason causing the loss of cultivar resistance of wheat and sexual reproduction is a major way of new races production.More recently,foreign and domestic studies reported that barberry(Berberis spp.)and Mahonia(only M.aquifolium)served as alternate hosts for Pst.In many regions of China,Pst completes sexual reproduction on susceptible Berberis species plants under natural conditions.Importantly,these susceptible barberry plants play roles not only in providing aeciospores as primary inoculums,but also in releasing new races to wheat fields.Whereas,it is not clear whether Mahonia species distributing in China can serve as alternate hosts for Pst.As an independent epidemic region of wheat stripe rust in China,Xinjiang is represented by a high genetic diversity of Pst population and wide distribution of Berberis species;however,it is unknown whether they are alternate hosts for Pst.Therefore,in this study,field investigations on Mahonia species in some provinces of China and Berberis species in Xinjiang as well as their geographic distribution were conducted.Whether the collected Mahonia and Berberis species can serve as alternate hosts for Pst were identified in laboratory.The results will facilitate to make management strategy for wheat stripe rust and provide scientific guide to the disease control in China.Interaction between Pst and wheat have been thoroughly and well studied,while few studies were reported regarding the interaction between Pst and its alternate host barberry.NPR1 gene is a key gene and plays important roles in plant defense response.In the present study,NPR1 homologue gene derived from barberry were cloned and designated as BhNPR1.Expression patterns of BhNPR1 and its downstream pathogenesis-related genes were investigated and analyzed.The result provided a basis for further understanding of the interaction between Pst and barberry.The main results are as follows:1.Field investigations showed many Mahonia species were distributed in different provinces and grew under various environmental conditions.Surveys on species and geographic distribution of Mahonia were performed in Gansu,Shaanxi,Sichuan,Yunnan,Guizhou,Guangxi,Hubei in which wheat stripe rust occurs.Based on biological identification,19 Mahonia species were identified and 10 of them were determined to biological species,including Mahonia bealei,M.eurybracteata Fedde subsp.eurybracteata,M.bodinieri Gagnep.M.fortunei(Lindl.)Fedde,M.duclouxiana Gagnep.,M.microphylla Ying et G.R.Long,M.nitens Schneid.,M.eurybracteata subsp.ganpinensis(Levl)Ying et Boufford.,M.retinervis Hsiao et Y.S.Wang,and M.sheridaniana Schneid.Six Mahonia species collected,including two from Gansu,one from Sichuan(Mahonia sp.),one from Guizhou,one from Hubei and one from Guangxi were not identified to specific species due to lack of flowers and seeds during surveys.2.Mahonia species tested exhibited different responses to Pst infection.Of nine Mahoina species challenged withPst basidiospores developed from germinated teliospores,three Mahonia species,M.fortune,M.eurybracteata subsp.Ganpinensis,and M.sheridaniana,can be infected by the stripe rust pathogen.The resultant aeciospores successfully infected wheat susceptible cultivar Mingxian 169 and produce uredia.This indicated that they could serve as alternate hosts for Pst.Another three Mahonia species,including M.bealei,M.retinervis and an unknown Mahonia sp.collected from Sichuan,represented moderately resistant to Pst with symptoms of infection specks and without aecia production after inoculation.This hinted the three Mahonia species were not alternate hosts for the stripe rust pathogen.M.bodinieri,M.duclouxiana,and M.microphylla showed immune or highly resistant to Pst and produced merely small chloric lesions or no symptom in three repeated tests,indicating that they were not able to serve as alternate hosts for Pst.3.Based on field investigations,three Berberis species were found in major wheat production regions of Xinjiang,and characterized by a large quantity and wide geographic distribution.All of these three Berberis species were identified as alternate hosts for Pst.Field surveys on Berberis species in Xinjiang were carried out in winter wheat region(A’kesu)and spring wheat regions involving Urumqi,Yili Valley,Changji and Qitai.In light of biological characteristics,three Berberis species including B.heteropoda,B.nummularia,and B.kaschgarica were identified.In Yili and Changji regions,Berberis bushes were found in many surveyed sites and B.heteropoda was the most widespread Berberis species.Furthermore,all of these three Berberis species could be successfully infected by the rust pathogen and the resultant aeciospores could infect wheat cultivar Mingxian 169,suggesting that they were alternate hosts for Pst.4.BhNPR1 and its downstream pathogenesis-related genes were not induced during the Pst infection of barberry,suggested that they didn’t function in defense response to stripe rust infection,which may cause defectives in barberry innate immune system and explain that barberry act as a common host for rust fungi.In this study,NPR1 homologue in barberry,designated as BhNPR1,was cloned.Expression patterns of BhNPR1 and its downstream pathogenesis-related genes were analyzed.Unlike the induction of wheat NPR1 upon Pst urediospores infection,the expression level of BhNPR1 remained almost constant during the infection by Pst basidiospores.In addition,the expression levels of BhPR5 and BhPDF1.2a remained unchangeable also,while BhPR1 and BhPR2 were significantly up-regulated during the Pst infection.