Effects Of Serendipita Indica On Growth And Drought Tolerance Of Banana(Musa Acuminate Cv. ‘Tianbaojiao’)

Banana（Musa spp.）,being originally native to o southeastern Asia,is an important fruit tree and food crop in the world.Water is essential for the growth of plants,and long-term insufficient supply of water limits the root development and plant growth severely.Serendipita indica,is an endophytic fungus,which can produce good growth-promoting and anti-synergic effects after colonization on plant roots.In this study,the effects of S.indica on drought resistance of banana were studied.The growth status of bananas with-and without-S.indica colonization and the determination of related physiological and biochemical indexes under drought stress were observed.And RNA-seq of the root system of banana seedlings was performed,aiming at comparing the differential expression gene of banana seedings with-or without-S.indica colonization under drought stress,to identify the key drought-resistant gene of bananas in response to S.indica,and preliminarily explore the molecular mechanism of S.indica how improve banana drought resistance.The main findings are as follows:1.Effects of Serendipita indica on banana growth under drought stressThe phenotypic changes of banana seedlings with-and without-S.indica colonization under drought stress were observed.And growth indexes of leaf number,leaf area,plant height,stem diameter,root length and root number of banana seedlings were measured.The results showed that,only the number of leaves and stem diameter of banana seedlings with-S.indica colonization were significantly higher than those of the CK group when growing under normal water conditions,and there were no significant differences in other growth indicators.The main symptoms under drought stress showed that,the leaves wilted significantly,superimposed on the back,severely sagged,and leaf edge was curled and yellow,the seedlings had less green leaves.As a whole,the plants were dwarf and developed slowly.The phenotypic variation of seedlings with S.indica colonization were less severe than those of without-S.indica colonization,and the appearance of drought symptoms was slowly.The results indicated S.indica could alleviate the growth inhibition of drought on banana seedlings,the growth-promoting effect of S.indica on banana seedlings was more significant under drought stress,and it could promote the above-ground growth and root development of banana seedlings.2.Effects of Serendipita indica on physiology and biochemistry of banana under drought stressThe results showed that S.indica could improve the drought resistance of banana by improving the activity of POD in leaves and the activity of CAT in roots to degrade and remove harmful substances produced by drought stress.It also could reduce MDA accumulation in leaves and roots,promote the synthesis and accumulation of Pro and SS in leaves,slow down the decomposition of chlorophyll,and accelerate the synthesis and accumulation of ABA in leaves to enhance the drought resistance of banana under severe drought stress.3.Effects of Serendipita indica on gene expression in banana roots under drought stressIn order to identify the metabolic pathways and gene expression changes of S.indica under drought treatment,we combined transcriptome sequencing and differential expression analysis.Through the GO and KEGG analysis,it was found that S.indica could alleviate the inhibition of drought on banana growth and promote the growth under drought stress,regulated stomatal opening and closing,to improve banana drought resistance,mainly by regulating the differential expression of AUX22D,AUX22E,IAA4,IAA30,IAA16,BSK2,BSK1,TCH22,CYCD3-2,AHP2,RR22,RR1,TIFY9,TIFY10B,At5g57670,ETR2,EBF1,ERF1B,PYL3,PYL4,AHG1,PP2C53,PP2CA,SAPK7 and ABF2.S.indica also affected the synthesis of scopolin,coumarine,lignin and other phenylpropylene compounds by upregulating most genes in the phenylpropanoid biosynthesis pathway,such as PAL3,4CLL5,CYP73A12,PHT1,OMT2,COMT,HOMT1,TOGT1,BGLU12,BACOVA＿02659.Also,S.indica took part in the regulation of POD activity,induced the specific expression of NPK1.In conclusion,by regulating the above genes expression,S.indica regulated the H₂O₂ content,maintained the homeostasis of ROS,to improve the drought resistance of bananas.