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