**Jia Zhao, Xu Zhang, Wentao Wan, Heng Zhang, Jia Liu, Mengli Li, Haiyan Wang, Jin Xiao \* and Xiue Wang \***

State Key Laboratory of Crop Genetics and Germplasm Enhancement, Cytogenetics Institute, Nanjing Agricultural University/JCIC-MCP, Nanjing 210095, China; 2015201054@njau.edu.cn (J.Z.); 2018201061@njau.edu.cn (X.Z.); 2016201003@njau.edu.cn (W.W.); 2016201031@njau.edu.cn (H.Z.); 2018201063@njau.edu.cn (J.L.); 2016101134@njau.edu.cn (M.L.); hywang@njau.edu.cn (H.W.)

**\*** Correspondence: xiaojin@njau.edu.cn (J.X.); xiuew@njau.edu.cn (X.W.); Tel.: +86-25-8439-9893 (J.X.); +86-25-8439-5308 (X.W.)

Received: 18 November 2018; Accepted: 21 December 2018; Published: 24 December 2018

**Abstract:** The *EXO70* gene family is involved in different biological processes in plants, ranging from plant polar growth to plant immunity. To date, analysis of the *EXO70* gene family has been limited in *Triticeae* species, e.g., hexaploidy *Triticum aestivum* and its ancestral/related species. By in silico analysis of multiple *Triticeae* sequence databases, a total of 200 *EXO70* members were identified. By homologue cloning approaches, 15 full-length cDNA of *EXO70s* were cloned from diploid *Haynaldia villosa*. Phylogenetic relationship analysis of 215 *EXO70* members classified them into three groups (*EXO70.1*, *EXO70.2*, and *EXO70.3*) and nine subgroups (*EXO70A* to *EXO70I*). The distribution of most *EXO70* genes among different species/sub-genomes were collinear, implying their orthologous relationship. The *EXO70A* subgroup has the most introns (at least five introns), while the remaining seven subgroups have only one intron on average. The expression profiling of *EXO70* genes from wheat revealed that 40 wheat *EXO70* genes were expressed in at least one tissue (leaf, stem, or root), of which 25 wheat *EXO70* genes were in response to at least one biotic stress (stripe rust or powdery mildew) or abiotic stress (drought or heat). Subcellular localization analysis showed that ten EXO70-V proteins had distinct plasma membrane localization, EXO70I1-V showed a distinctive spotted pattern on the membrane. The 15 *EXO70-V* genes were differentially expressed in three tissue. Apart from *EXO70D2-V*, the remaining *EXO70-V* genes were in response to at least one stress (flg22, chitin, powdery mildew, drought, NaCl, heat, or cold) or phytohormones (salicylic acid, methyl jasmonate, ethephon, or abscisic acid) and hydrogen peroxide treatments. This research provides a genome-wide glimpse of the *Triticeae EXO70* gene family and those up- or downregulated genes require further validation of their biological roles in response to biotic/abiotic stresses.

**Keywords:** EXO70; *Haynaldia villosa*; gene family; phylogenetic relationship; subcellular localization; expression profiling
