Identification of LBD gene family in Xanthoceras sorbifolium and its response to salt stress

【Objective】The members of the lateral organ boundary domain（LBD）gene family of Xanthoceras sorbifolium were identified and their expression analysis under salt stress conditions were analyzed，which provided theoretical basis for the breeding of stress-resistant varieties of X. sorbifolium and its promotion and utilization in saline-alkali land. 【Method】Based on the complete genome data of X. sorbifolium，the members of LBD gene family were identified from the X. sorbifolium genome database. The physicochemical properties，conserved motifs，cis-acting elements，gene structure and phylogenetic relationships of the XsLBD family proteins were predicted and analyzed using bioinformatics tools such as ExPASy and MEME. The 2-month-old seedlings of X. sorbifolium were treated with NaCl concentrations of 50， 100 and 150 mmol/L，with 0 mmol/L NaCl as the control group（CK）. The expression patterns of XsLBD family genes in the roots and leaves of X. sorbifolium under salt stress were detected by real-time fluorescence quantitative PCR.【Result】 A total of 43 gene family members were identified from X. sorbifolium genome，and were named XsLBD1-XsLBD43. XsLBD family proteins encoded 138-404 amino acid residues，with a theoretical isoelectric point（pI）of 4.60-9.75，molecular weight of 15696.60-44476.88 kD，and subcellular localization results showed that all but XsLBD4，XsLBD8， XsLBD9 and XsLBD20 proteins were localized in the cell nucleus. There were 42 XsLBD family genes distributed on 13 chromosomes，while XsLBD43 gene was located outside of the chromosomes. Based on the amino acid sequence similarities of LBD from X. sorbifolium，Arabidopsis thaliana，Oryza sativa and Populus tomentosa，the 178 LBD family proteins were divided into 2 major groups（Class I and Class II），with 38 XsLBD family proteins in Class I. The exon number of XsLBD gene family members ranged from 1 to 5，while the intron number ranged from 0 to 4. All XsLBD family proteins contained Motif 2 and Motif 3. The promoters of XsLBD family genes contained response elements to hormones （salicylic acid，abscisic acid，auxin），stresses（cold，drought induction），and plant growth and development（seedspecific regulation and circadian rhythm control）. Among the 13 XsLBD family genes screened out，12 and 11 genes showed significant differences（P<0.05，the same below）in relative expression levels in roots and leaves compared with CK after different concentrations of NaCl salt stress treatment respectively. Among them，the relative expression level of XsLBD42 gene in roots and leaves was about 40 times higher than that of CK.【Conclusion】A total of 43 XsLBD gene family members were screened，which have relatively simple structures and certain conservativeness；XsLBD family genes are involved in regulating the growth and development，metabolism and stress response of X. sorbifolium； XsLBD9，XsLBD11，XsLBD23 and XsLBD42 may play an important role in the salt stress response of X. sorbifolium.