Comparative Transcriptome Analysis Of Eggplant Responses To Salt Stress And Functional Identification Of The Candidate Gene SmAKT1

Soil salinization is one of the most crucial abiotic stresses that limit plants growth.There are approximately one-third of the total irrigated agricultural land is salinized and about 100 million ha land is tidal flats and saline-alkali wasteland in China.Studying the salt-tolerant molecular mechanisms in plants is very beneficial for the sustainable production of crops in salinized areas.Eggplant(Solanum melongena L.)is one of the main solanaceous vegetable cultivated and consumed worldwide.The existing researches in eggplant were focused on salt-induced morphological,biochemical and physiological changes,while salt-tolerant molecular mechanisms in eggplant unclearly.Therefore,in order to promote the sustainable production of eggplant in salinized areas,the salt-tolerant eggplant materials were screened out and the salt-tolerant molecular mechanisms were explored in this paper.The main results are as follows:1)In order to avoid seed itself defects,uniformly germinated eggplant seeds were selected and treated with salt stress.With the increase of NaCl concentration,the growth of eggplants was inhibited more seriously.But significant differences were found among different eggplant materials.The subordinate function method was used to comprehensive four indicators to sort the salt tolerance of the 19 eggplant materials.Based on the results of early embryo growth stage,the salt tolerance on the seedling stage of part eggplant varieties were studied.The results suggested that the relationship of salt tolerance between the two growth stages was not close.Strikingly,on both the two growth stages,the eggplant material Zhusiqie(No.118)showed highest salt tolerance,while Hongqie(No.30)showed salt sesentivity.2)Salt-tolerance analysis between the salt-tolerant eggplant No.118 and salt-sensitive eggplant No.30 showed that less damaged on growth and higher K~+/Na~+ratios in No.118 leaves than those of No.30.Consequently,they were re-named the two eggplant materials as ST118 and SS30,respectively.Then,comparative-transcriptome analysis was used as a powerful approach to understand the salt-response mechanisms in the leaves and roots of SS30 and ST118.And it revealed that genotype-specific and organ-specific manners exist in eggplant in response to salt stress.Strikingly,the genotype-specific differentially expressed genes(DEGs)in ST118 were considered crucial to its higher salt-tolerance,because the expression patterns of common DEGs in the leaves/roots of the two eggplant genotypes were almost the same.Further analysis found that five transcription factors,which have been reported to be in response to elevated external salinity,showed different expression pattern between ST118 and SS30,including two NACs,one WRKY,one MYB and C2C2-CO-like.In addition,there were seven K~+transporters while only one Na~+transporter were significantly regulated by salt stress,and the AKT1,KAT1 and SOS1 were only up-regulated in the leaves of ST118.These results implied that the K~+transporters were very important for maintaining K~+and Na~+homeostasis and distribution in plants under salt conditions.3)The salt tolerant candicate gene SmAKT1 was cloned from eggplant.The amino acid sequence alignment and phylogenetic tree analysis showed that SmAKT1and AKT1s from other plant species were highly conserved.In addition,the subcellular localization assay in tobacco leaves showed that SmAKT1 was only expressed at the plasma membrane,and the tissue-specific analysis found that it was mainly expressed in eggplant roots.These results indicated SmAKT1 could regulate K~+absorption in cells.Both the low-K~+and salt stress could induce SmAKT1expression,and the expression patterns under the two stresses were similar.SmAKT1could not only complement the growth of yeast K~+defect mutant strain and rescue the low-K~+-sensitive phenotype of Arabidopsis akt1 mutant under low-K~+stress,but also enhance the growth of them under salt stress.These results demonstrated that SmAKT1 not only has K~+uptake activity but also play an important role on improving salt-tolerance.4)Calcineurin B-like proteins(CBLs)are calcium sensors and control the affinities and activities of numerous ion transporters with CBL-interacting protein kinases(CIPKs).And it has been reported that CBLs and CIPKs gene families were the regulators of AKT1.Here,a total of 5 SmCBL and 15 SmCIPK genes were firstly identified from eggplant genome database.And the amino acid sequence alignment and phylogenetic tree analysis were used for further confirmation.The tissue-specific analysis found that 5 SmCBLs and 12 SmCIPKs were mainly expressed in eggplant roots,and they were induced or inhibited by different ion stresses.The yeast two-hybrid(Y2H)assay and bimolecular fluorescence complementation(BiFC)assay were used to explore the interaction network between SmCBLs and SmCIPKs,and some new CBL-CIPK complexes were found which have never been discovered in any other plant species.In summary,this study provided the theoretical foundation for studying the mechanisms of SmCBL-SmCIPK complexes in improving the salt tolerance of eggplants.