Evolutionary And Response Analysis Of BZIP Genes In Strawberry Under Drought Stress

The fruit of strawberry has a strong aroma.However,more extreme temperatures,droughts,severe fungal infections and secondary salinization greatly limit the growth,reproduction and yield of strawberries.Since the perennial strawberry genome is relatively small,it is generally considered a new model plant in Rosaceae.Transcription factors,usually have a specific binding with cis-elements located in the eukaryotic gene promoter region,and thus enhance or inhibit the transcription efficiency of genes to regulate gene expression levels.The transcriptional regulation of gene expression plays a key role in controlling many important biological processes,such as cell morphogenesis,growth and development,metabolism,physiological balance and environmental stress response.The bZIP(basic leucine zipper)transcription factor family is a relatively large and conservative family,but the gene family studies in strawberry are still very few.The completion of the strawberry genome sequencing work laid the foundation for a comprehensive analysis of bZIP biological function at its genome level.In the present study,50,116 and 47 bZIP genes were identified in strawberry,apple and peach,respectively.Species-specific duplication was the main contributor to the large number of bZIPs observed in apple.After WGD in apple genome,orthologous bZIP genes corresponding to strawberry on duplicated regions in apple genome were retained.However,in peach ancestor,these syntenic regions were quickly lost or deleted.The analysis of orthologous pairs between chromosomes indicates that these orthologs derived from one gene duplication located on one of the nine ancient chromosomes in the Rosaceae.Maybe the positive selection contributed to the expansion of clade S to adapt to the development and environment stresses.In addition,purifying selection was mainly responsible for bZIP sequence-specific DNA binding.The comparative analysis of bZIP genes in three species provides information on the evolutionary fate of bZIP genes in apple and peach after they diverged from strawberry.bZIP genes are known to play a crucial role in response to various tissues development in plant,as well as abiotic or biotic stress challenges.We have performed an identification and characterization of 50 bZIP genes across the woodland strawberry genome,which were divided into 10 clades according to the phylogenetic relationship of the strawberry bZIP proteins with those in Arabidopsis and rice.Five categories of intron patterns(a,b,c,d and e)are observed within basic and hinge regions of their bZIP domains.Some addtional known conserved motifs have been found by detailed sequence analysis and present the group specificity.Further,we predicted DNA-binding specificity of basic and hinge regions as well as dimerization properties of leucine zipper regions,which was consistent with our phylogenetic clade and classified into 20 subfamilies.Across the different developmental transcriptome data of fruits,the clade A bZIPs members showed different tissue-specific expression patterns and the duplicated genes were differentially regulated,indicating a functional diversification coupled with the expansion of this gene family in strawberry.Under normal growth conditions,mrna 11837 and mrna30280 of clade A showed very weak expression levels in organs and fruits,respectively;but higher expression was observed with different set of genes following drought and heat treatment,which may be caused by the separate response pathway between drought and heat treatments.The evolutionary relationship of the GBF(G-box binding factors)gene family across the green plants was investigated using a comparative phylogenetic framework.GBF candidate genes are present in 37 green plants,including a moss,monocots,and eudicots.Phylogenetic analysis revealed the evolutionary division of the GBF gene family into nine major clades,and GBFs of clades 1,6 and 9 were located in the core eudicots.A novel domain,MFMR_assoc located between the MFMR and bZIP domain,was identified to be specific to GBF proteins of monocots and eudicots.There is a eudicot wide GBF gene expansion,which appears to have been mainly caused by MFMR_assoc domain with relaxed purifying selection or positive selection followed by species-segmental duplication and tandem duplication.The observed diversity of MFMR_assoc domain among the core eudicots clades might enable the changes in gene function among paleoduplicated genes.We can conclude that the MFMR_assoc domains with relaxed purifying selection or positive selection maybe contribute to functional diversity in the processes of GBF protein synthesis and target gene transactivation.The diploid woodland strawberry is being recognized as a model for studying the Rosaceae family,which contains many economically important fruit trees and ornamental plant.However,various abiotic stresses are the major constrains affecting its overall productivity.To discovery candidate genes related to abiotic stress responses,we performed RNA sequencing for transcritome profiling of old and young leaves of strawberry seedling under drought treatment.In total,we got more than 1186 billion clean reads from control and treated tissue samples.Data analyses provided a comprehensive view of the dynamic transcriptional response of different tissues to droughts in strawberry.Differential expression analysis identified a total of 6992 DEGs showing response to D7/D1,D5/D1 and D3/D1 between old and young leaves.The reference-based transcriptome assembly was generated and at least 736 novel genes expressed under drought stress conditions were identified.We observed extensive genes involved in metabolic pathways,biosynthesis of secondary metabolites,strarch and sucrose metabolism,and plant hormone signal transduction under drought.In addition,10 genes contained G-box cis-elements in their promoters were identified to have a consistency with 3 FvbZIP genes with high expression level under drought.The comprehensive transcriptome analyses presented in this study revealed several potential key regulators of strawberry response to abiotic stresses and open avenues to carry out functional and applied genomic studies for improving drought tolerance in strawberry.