Influence of plant growth regulators on Expansin2 expression in strawberry fruit. Cloning and functional analysis of FaEXP2 promoter region

• The influence of plant growth regulators on the expression of FaEXP2 was analyzed.
• FaEXP2 is positively regulated by abscisic acid and negatively by auxins.
• A small promoter (pFaEXP2-650) was isolated from strawberry.
• The promoter activity is receptacle-specific and increases during ripening.

FaEXP2 encodes a fruit-specific expansin that is known to be associated with cell wall loosening and fruit softening in strawberry (Fragaria × ananassa Duch.). In spite of its relevant role in fruit ripening, little is known about the hormonal regulation of this gene. In the present study, we isolated a 650 bp fragment of the FaEXP2 gene promoter and the in silico analysis revealed the presence of cis-acting elements associated with hormones, light and stress-related responses. With the aim of characterizing the hormonal regulation of FaEXP2 expression, strawberry fruit were treated with plant growth regulators and changes in transcript levels were analyzed by qPCR. FaEXP2 expression levels were significantly higher than control in fruit treated with abscisic acid (ABA), and when the endogenous source of auxins (achenes) was removed. In contrast, transcript accumulation was not affected by exogenous applications of gibberellic acid (GA3), naphtalenacetic acid (NAA), ethylene or 1-methylcyclopropene (1-MCP). Also, functional analysis of FaEXP2 gene promoter was performed by transient and permanent strawberry transformation. Histochemical GUS staining analysis showed that the 650 bp-promoter fragment was able to drive the reporter gene expression specifically to the receptacle and along ripening. Our results provide new insights into the hormonal regulation of FaEXP2 expression.