| Summary: | Dirigent proteins (<i>DIR</i>) play important roles in the biosynthesis of lignins and lignans, defensive responses, secondary metabolism, and disease resistance in plants. The <i>DIR</i> gene family has been identified and studied in many plants. However, the identification of <i>DIR</i> gene family in eggplant has not been conducted yet. Therefore, in this study, based on the available genome information of eggplant, the <i>DIR</i> family genes in eggplant were identified with bioinformatics methods. The expression pattern analyses of eggplant <i>DIR</i> family genes in different organs and stresses were also conducted to understand their biological functions. The results showed that a total of 24 <i>DIR</i> genes were identified in the eggplant, which were divided into three subfamilies (<i>DIR</i>-<i>a</i>, <i>DIR</i>-<i>b/d</i>, and <i>DIR</i>-<i>e</i>). Synteny analysis of <i>DIR</i> genes among eggplant, <i>Arabidopsis</i>, and rice showed that 15 eggplant <i>DIR</i> genes were colinear with 18 <i>Arabidopsis DIR</i> genes, and 16 eggplant <i>DIR</i> genes were colinear with 15 rice <i>DIR</i> genes. Phylogenetic tree analysis showed that 19 pairs of orthologous genes were identified between eggplant and pepper. The <i>cis</i>-acting elements analysis implied that the eggplant <i>DIR</i> genes contained a lot of <i>cis</i>-elements associated with stress and hormone response. The organ-specific expression analysis of eggplant <i>DIR</i> family genes revealed that only the <i>SmDIR3</i> gene was highly expressed in all the 19 organs of eggplant. Some <i>SmDIR</i> genes, including <i>SmDIR7</i>, <i>SmDIR8</i>, <i>SmDIR11</i>, <i>SmDIR14</i>, <i>SmDIR18</i>, <i>SmDIR19</i>, <i>SmDIR20</i>, and <i>SmDIR23</i>, were not or were lowly expressed in the eggplant organs, while the other eggplant <i>DIR</i> family genes showed an organ-specific expression pattern. Furthermore, 19 of 24 <i>SmDIR</i> genes were differentially expressed in response to abiotic and biotic stresses. 5 <i>SmDIR</i> genes, including <i>SmDIR3</i>, <i>SmDIR5</i>, <i>SmDIR6</i>, <i>SmDIR12</i>, and <i>SmDIR22</i>, were differentially expressed under multiple types of abiotic and biotic stresses. Especially notable, the <i>SmDIR22</i> gene was differentially expressed under three types of abiotic stresses and two types of biotic stresses, which indicated that the <i>SmDIR22</i> gene plays an important role in the response to abiotic and biotic stresses. These results provide valuable evidence for a better understanding of the biological role of <i>DIR</i> genes in eggplant.
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