A GH3-like gene, LaGH3, isolated from hybrid larch (Larix leptolepis × Larix olgensis) is regulated by auxin and abscisic acid during somatic embryogenesis

Abstract

A Gretchen Hagen 3-like gene, LaGH3 from hybrid larch (Larix leptolepis × Larix olgensis), was identified, and the effects of abscisic acid (ABA) and indole-3-acetic acid (IAA) on its transcriptional levels and expression patterns during somatic embryogenesis were analyzed. A full-length cDNA sequence of a Gretchen Hagen 3 (GH3) gene was isolated from hybrid larch (Larix leptolepis × Larix olgensis) and designated LaGH3. The cDNA was 2053 bp in length and contained an 1848-bp open-reading frame encoding a predicted protein of 615 amino acids, characterized by four conserved motifs of the GH3 protein family: P-loop, α5, α6, and β8–β9. The 5′-flanking promoter region of LaGH3 was cloned using an improved TAIL-PCR technique. In this region, we identified several auxin- and abscisic acid (ABA)-inducible elements. Expression analysis showed that LaGH3 was induced by indole-3-acetic acid and that its transcript accumulation was inhibited by ABA. Further experiments demonstrated that ABA was the main factor in LaGH3 downregulation during the early stage of somatic embryogenesis, although the absence of auxin decreased LaGH3 expression slightly. LaGH3 transcripts gradually increased and peaked at 28 days with the rapid development of somatic embryos and then declined as the somatic embryos matured. We suggest that the level of LaGH3 transcripts partly represents the dynamics of endogenous auxin during somatic embryo development in larch. Taken together, our results provide evidence that GH3 genes play important roles in the crosstalk between auxin and ABA by maintaining auxin homeostasis during somatic embryo development.