Identification and Expression Analysis of Gretchen Hagen 3 (GH3) in Kiwifruit (Actinidia chinensis) During Postharvest Process

Abstract

In plants, the Gretchen <i>GH3</i> (GH3) protein is involved in free auxin (IAA) and amino acid conjugation, thus controlling auxin homeostasis. To date, many <i>GH3</i> gene families have been identified from different plant species. However, the <i>GH3</i> gene family in kiwifruit (<i>Actinidia chinensis</i>) has not been reported. In this study, 12 <i>AcGH3</i> genes were identified, phylogenetic analysis of AtGH3 (<i>Arabidopsis</i>), SlGH3 (<i>Solanum lycopersicum</i>), and AcGH3 provided insights into various orthologous relationships among these proteins, which were categorized into three groups. Expression analysis of <i>AcGH3</i> genes at different postharvest stages suggested limited or no role for most of the <i>AcGH3</i> genes at the initiation of fruit ripening. <i>AcGH3.1</i> was the only gene exhibiting ripening-associated expression. Further study showed that the expression of <i>AcGH3.1</i> gene was induced by NAA (1-naphthylacetic acid, auxin analogue) and inhibited by 1-MCP (1-methylcyclopropene, ethylene receptor inhibitor), respectively. <i>AcGH3.1</i> gene silencing inhibited gene expression and delayed fruit softening in kiwifruit. The results indicate that <i>AcGH3.1</i> may play an important role in the softening process of fruits. Analysis of the <i>AcGH3.1</i> promoter revealed the presence of many cis-elements related to hormones, light, and drought. The determination of GUS (β-Galactosidase) enzyme activity revealed that promoter activity increased strikingly upon abscisic acid (ABA), ethylene, or NAA treatment, and significantly decreased with salicylic acid (SA) treatment. The present study could help in the identification of <i>GH3</i> genes and revelation of <i>AcGH3.1</i> gene function during postharvest stages, which pave the way for further functional verification of the <i>AcGH3.1</i> gene.