The Response Of Banana (Musa Spp.) Hemicellulose To Mild Chilling Stress

Banana（Musa spp.）is the most important fruit and food crop in the tropical and subtropical regions.It is highly sensitive to low temperatures stress and frequently suffered from chilling injury in our country.Plant cell walls form the first defense line upon different stresses.Many studies have shown that cell wall components such as pectinand structural proteins play an important role in plant cold adaptation.The studies on the relationship between hemicellulose and the cold resistance of plants focus on the changes in the hemicellulose content of fruits during storage at low temperatures.No studies are involved in the expression and function of the related genes in plant tolerance to low temperatures.For better understanding the function of hemicelluloses in plants upon low temperature stress and mechanism underlying,we carried out the present study.In the present study,digital gene expression profiling（DGE）was employed to reveal the gene expression levels,especially those genes related to hemicellulose metabolism,in banana to low temperature stresses using chilling-sensitive cultivar ’Baxijiao’（Musa spp.AAA）as plant material.In additional,different changes in some chilling related physiological parameters,hemicellulose content,the expression of some genes involved in hemicellulose metabolism,as well as the temporal and spatial distribution of different types of hemicellulose between two cultivars（’Baxijiao’ and chilling-tolerant cultivar Musa spp.ABB cv.Dongguandajiao）were investigated and compared.The main results obtained are showed as follows:1.DGE analysis: 1933 genes were differentially expressed at low temperature of 16℃.Among them,978 and 955 genes were up-regulated and down-regulated respectively.Low-temperature stress at 10℃ resulted in 1267 genes differentially expressed（DEGs）,of which 724 ones were up-regulated and 543 ones were down-regulated.There were 40 DEGs involved in hemicelluloses metabolism,such as mannan synthase.Gene ontology（GO）annotations found that up-regulated DEGs were significantly enriched in 61 GO items while down-regulated DEGs were significantly enriched in 22 GO items;including some GO items related to biosynthesis and degradation of sugars.Kyto encyclopedia of genes and geneomes（KEGG）analysis showed that all DEGs obtained could be assigned to 114 KEGG metabolic pathways.Twelve out of these 114 KEGG metabolic pathways were significantly enriched,such as carbon fixation in photosynthetic organisms,starch and sucrose metabolism.2.Chilling-related physiological parameters: the relative electrical conductivity and the leaf damage rate of ’Baxijiao’ and ’Dongguandajiao’ increased under low-temperature stress,with relatively higher levels in ’Baxijiao’.When the temperature dropped to 10℃,the relative water content decreased in both cultivars,with relatively higher level in the chilling-tolerant cultivar ’Dongguandajiao’.3.Under low temperature stress,the change trend of the hemicellulose content in the chilling-sensitive cultivar ’Baxijiao’ leaves was different from the chilling-resistant cultivar ’Dongguandajiao’.The hemicellulose content in the ’Baxijiao’ leaves gradually decreased with the decrease of temperature.When the temperature dropped from 16℃ to 10℃,the reduction reached a significant level.The hemicellulose content in leaves of ’Dongguandajiao’ increased rapidly at the early stage of temperature dropping and then decreased with the dropping of temperature.4.Changes of hemicellulose metabolic-related gene expression under low temperature stress: DGE analysis showed that there were 11 and 29 DEGs related to hemicellulose biosynthesis and degradation in ’Baxijiao’ upon low temperature stress,and the different expression levels of seven genes out of them between the chilling-sensitive and tolerant cultivars were investigated with qPCR.The expression level of GSMUA_Achr11G09120₀01 in chilling-tolerant cultivar ’Dongguandajiao’ under low temperatures was always higher than that in the chilling-sensitive cultivar.The expression level of GSMUA_AchrUn_randomG25760₀01 in the chilling-sensitive cultivar ’Baxijiao’ decreased as the temperature decreased,while it was on the contrary for ’Dongguandajiao’,suggesting that these two genes involved inchilling-tolerance of bananas.5.Different responses of different hemicelluloses components to chilling stress: at low temperaturees,the antigens recognized by LM6 and CCRC-M126 antibodies were higher in the chilling-tolerant cultivar ’Dongguandajiao’ than the chilling-sensitive ?Baxijiao?,indicating that they related to the chilling-tolerance of bananas.The antigen recognized by antibodies of CCRC-M107,CCRC-M126 and CCRC-M131 increased in two cultivars upon low temperature stresses.The antigens recognized by antibodies of CCRC-M26,CCRC-M104 and LM21 didn’t change significantly at low temperature.