Physiological Response And Transcriptome Analysis Of Two Species In Indigofera Bungeana To Drought Stress

Breeding of drought-tolerant and good-quality forage plants is of great significance to the development of the livestock industry.Indigofera bungeana Walp.is a legume that can be developed and utilized as a high-quality protein forage grass.However,there is a lack of research on the physiological mechanism of Indigofera bungeana,and there are no relevant reports on transcriptome sequencing analysis under drought stress.In this study,Indigofera bungeana cultivated species and wild species were used as tests to give continuous drought stress for 13 d,and when the soil water content was as low as 20%field water holding(field capacity,FC)and rehydration to 70-80%FC.By comparing the growth and physiological and biochemical index changes of two kinds of Indigofera bungeana under drought stress+rehydration and normal irrigation,and combining with transcriptomic analysis,the physiological and molecular response mechanism of two kinds of Indigofera bungeana to drought stress was explored,which provided experimental reference for cultivating new varieties with excellent stress resistance.The main study results are presented as follows:(1)With the intensification of drought stress,the height,branch number,leaf area,specific leaf area and biomass of the two species of Indigofera bungeana strains were significantly reduced,and the root-crown ratio was significantly increased.The total root length,total surface area,and number of bifurcations were significantly decreased,and the stomatal density and stomatal aperture were significantly decreased.After rehydration treatment,all parameters of the two Indigofera bungeana species were recovered to control levels except for the root characteristics.Among them,the variation of the parameters of the cultivated species was greater than that of the wild specie.(2)With the increase of drought stress,the relative water content,starch content,active ethylene content and chlorophyll content of wild species were significantly decreased;the physiological indexes such as relative conductivity,malondialdehyde,proline,hydrogen peroxide,catalase activity increased significantly;the sucrose content,sucrose synthase activity,amylase activity,abscisic acid,and auxin content all significantly increased.After rehydration treatment,all other indexes returned to the control level except for malondialdehyde content.Among them,the content of hydrogen peroxide,chlorophyll a,b,α-amylase activity and ethylene were significantly higher than that of wild Indigofera bungeana.(3)After correlation and principal component analysis,the two Indigofera bungeana growth parameters and ground biomass were significantly positively correlated with root structure characteristics and chlorophyll content.Underground biomass was significantly and positively correlated with stomatal morphological characteristics and relative water content.The root crown ratio was significantly positively correlated with root structure characteristics and endogenous hormone content.The contribution of stomatal aperture,auxin content,and abscisic acid content contributed 46.3%in response to drought stress,and relative water content,catalase activity,and proline content contributed 23.3%.(4)Through transcriptome analysis,6090 and 9309 differential genes were identified in blue leaves and roots of wild species,respectively;3830 and 6502 differential genes were identified in cultivated leaves and roots,respectively.The transcription factors with the highest expression of common enrichment in the two Indigofera bungeana species were:ethylene response factor,basic/helix-loop-helix,basic leucine zipper,and v-myb avian myeloblastosis virus oncogene homologs.KEGG enrichment analysis found that three pathways were significantly enriched in phytohormone signaling,MAPK-plant signaling,and starch and sucrose metabolism.Among the enriched differential genes,differential genes such as serine/threonine phosphatase 2C,SNF 1-related protein kinase 2,auxin small RNA and ethylene receptor 1 were significantly enriched in plant hormone signaling;genes such as respiratory burst oxidase and catalase were differentially expressed in MAPK-plant signal transduction,and genes such as sucrose synthase,neutral invertase and α-amylase are involved in the synthesis and degradation of sucrose and starch.In conclusion,the two species of Indigofera bungeana can resist drought stress mainly by regulating stomatal movement,inhibiting root growth,regulating osmotic substances and endogenous hormone content,and enhancing antioxidant capacity.