Effect And Preliminary Mechanism Of Arbuscular Mycorrhizal Fungi On Drought Resistance In Vaccinium Corymbosum

Over the past decades,many areas of China have invested in blueberry culture,China has the potential to become one of the largest blueberry-producing countries in the world.However,drought have severely affected blueberry growth and production in areas of Yangtze River.In this study,two southern highbush blueberry cultivars i.e.‘Misty' and ‘O'Neal‘(Vaccinium corymbosum)were taken as materials,the effects and mechanisms of arbuscular mycorrhizal(AM)fungi inoculation on blueberry under drought stress were investigated in greenhouse condition.The influences of four AM fungi,Glomus mosseae,G.versiforme,G.intraradices,and G.etunicatum on southern highbush blueberry cultivar i.e.‘Misty' in response to drought stress(DS)were investigated.The results showed that DS decreased leaf relative water content(RWC)and chlorophyll content,increased soluble sugar and malondialdehyde(MDA)content and superoxide dismutase(SOD)activity,but had no significant effects on mycorrhizal colonization.Under DS conditions,leaf RWC,chlorophyll and soluble sugar contents,and SOD activity were significantly higher in AM-inoculated plants,especially in G.mosseae-inoculated plants than in non-AM-inoculated plants,while leaf MDA content was lower in the former.In addition,AM fungi,especially G.mosseae,increased phosphorus(P)and potassium(K)concentrations in the leaves,stems and roots of blueberry plants,as well as acid phosphatase,catalase and urease activities in rhizosphere soil of blueberry plants,in comparison with the non-AM-inoculated treatment.These results indicate that AM fungi inoculation may improve the drought tolerance of ‘Misty' blueberry by increasing the levels of antioxidant enzyme and osmotic adjustment,improving the soil environment,accompanied by increases in P and K uptake by plants;G.mosseae is the most beneficial Glomus among four AM fungi to enhance the resistance of ‘Misty' blueberry plants against DS.The effects of the AM fungi G.mosseae on the physiological metabolism of blueberry were studied under well-water(WW)and persistent moderate drought stress(MDS)conditions.Compare with control,AM inoculation significantly enhanced the contents of chlorophyll(a+b),carotenoid and magnesium(Mg),relative water content(RWC)and SOD activity in the leaves,as well as soluble sugar content and leaf SOD activity in the roots,while decreased the contents of proline and mineral elements such as K and calcium etc.in the leaves.Our results suggest that AM inoculation improve the protective enzyme activity and photosynthesis,resulting in the enhancement of blueberry in response to moderate drought tolerance.The main differences were observed in transcript profiles of blueberry under moderate drought stress and G.mosseae inoculation conditions using RNA-Seq technology.Filtering of the raw sequences resulted in above 124 453 391 high-quality(HQ)reads with an average length of 125 nucleotides,generating more than 51 Mb corresponding to about 90% of the raw sequence in the four treatments in blueberry.After assembled the HQ reads to Unigenes and annotated the function,the results showed,compare with WW & non-AMF plants,there are 1 128 differentially Unigenes expressed both in MDS and MDS & mycorrhizal plants,and 6 342,6 833 and 6 724 Unigenes expressed in mycorrhizal treatment,drought stress treatment and drought & mycorrhizal treatment,respectively.924 Unigenes of them might be associated with mycorrhizae,as well as 1 117 Unigenes of them might be related to drought stress.The up-regulated genes under mycorrhizal and drought stress & mycorrhizal conditions contained fifteen genes associated with transfer and signal regulation such as ABC transporter,thirteen genes associated with photosystem(PS)and carbohydrate such as PS? protein,fifteen genes associated with protease such as serine carboxypeptidase and twenty-six transcription factors and regulation such as methyltransferase.