The sequence characters of EXPANSIN genes and the analysis of their induced expression after the infection of root-knot nematodes in peach

Astract:【Objective】Expansins are plant cell-wall loosening proteins involved in cell enlargement and a variety of other developmental processes in which cell-wall modification occurs.Members of the expansin family of cell wall proteins disrupt hydrogen bonds within the cell wall polymer matrix and are implicated in cell wall polymer disassembly and cell elongation.The expansin encoding proteins belong to the cell wall zymoprotein, expressing in the plant with a high degree of specificity.Their expression and regulation are controlled not only by the developmental processes of plant, but also by exogenous hormones and environmental factors.Previous studies showed that expansin genes played important roles in plant seed germination, root growth, stem and leaf growth and development, fruit ripening and softening, and organ abscission root-knot nematodes invade host roots and induce formation of giant cell structures that serve them nutrients.The resistances of peach to root-knot nematodes vary with varities.'Honggengansutao 1' (Prunus kansuensis) is immune to Meloidogyne incognita.'Bailey' (Prunus persica) is highly susceptible to M.incognita.Studies revealed that nematodes changed expression of plant genes encoding cell wall modifying proteins including expansins.Expansins showed unique ability to induce cell wall extension in lower p H.This experiment aimed at exploring the role of expansin gene family during the interaction between peach roots and root knot nematodes.【Methods】The locations on the chromosomal information of the expansin gene family member were searched using the GDR, and the amino acid sequences of peach expansin family genes were obtained from the Phytozome.The estimated molecular weight and isoelectric point of the putative protein were obtained from the Ex PASY Compute p I/Mw.The amino acid sequences of the Arabidopsis thaliana expansin family were obtained from the TAIR database.The structures of expansin proteins were analyzed using the online tools of Gene Structure Display Server, and the maps were built using the software of Map Inspect.A multiple alignment analysis of peach expansin proteins was carried out using the Clustal X 2.1 program within the MEGA 5.0 software, and a phylogenetic tree between the peach and A.thaliana expansin proteins was constructed using the neighbor joining method and a bootstrap test was set at 1 000 to test the confidence of the tree.Additionally, seedlings of'Honggengansutao 1'and'Bailey'were inoculated with M.incognita using artificial indoor inoculation.Root tips were observed by staining at 0, 6, 12, 36, 60 and 84 h after inoculation.The expression levels of expansin genes of the seedlings of'Honggengansutao 1'and'Bailey'infected by M.incognita were detected using RNA-seq technique.【Results】27 expansin candidate genes were found in the peach genome.The lengths of them were typically 241-289 amino acids.The estimated molecular weights and isoelectric points of the putative proteins were 8.98-30.249 ku and 4.40-9.83.The proteins had two conserved domains, named as DPBB1 superfamily and Pollenallerg1 superfamily.A chromosome mapping analysis revealed that expansin genes distributed on 8 chromosomes.Chromosome 2 and 5 each had5 expansin genes.The results of an intron-exon structure analysis indicated that expansin gene family members were composed of 1-5 exons.Phylogenetic analysis indicated that peach expansin gene family was divided into two groups, ten EXPANSIN associated with giant cell forming proteins during nematode infection in A.thaliana belonged to EXPA subclass.We identified 7 081 differential expression genes through comparing the transcriptome of the immune accession'Honggengansutao 1' and the susceptible accession'Bailey'at 0, 6, 12, 36, 60 and 84 h after inoculation.3 380 genes were up-regulated and3 701 genes were down-regulated, respectively.Transcriptome analysis showed that the expression trends of the 10 expansin genes (ppa014051 m, ppa010203 m, ppa010260 m, ppa010198 m, ppa010654 m, ppa010180 m, ppa010226 m, ppa010379 m, ppa010067 m and ppa010443 m) were different in two different resistant germplasms.The expression level of ppa010314 m and ppa010226 m increased obviously in 'Bailey' as the infection by M.incognita and did not increased obviously in 'Honggengansutao 1', indicating that ppa010314 m and ppa010226 m might be the key genes for the formation of giant cell during the process of the infection by M.incognita.【Conclusion】These results suggested that the EXPANSIN gene family members be highly and structurally conserved.In peach, ppa010314 m and ppa010226 m may be involved in the interaction between peach roots and root knot nematodes.