Characterization and functional analysis of a MADS-box transcription factor gene (GbMADS9) from Ginkgo biloba

- A novel MADS-box gene, GbMADS9, was cloned and characterized in Ginkgo biloba.
- GbMADS9 is preferentially expressed in strobili and ovules of G. biloba.
- The expression of GbMADS9 in ginkgo was strongly induced by GA3, ABA, and abiotic stress.
- Overexpressing GbMADS9 in Arabidopsis promoted flowering and enhanced osmotic tolerance.

The MADS-box transcription factors play diverse roles in plant development, but little is known about the role of MADS-box genes in Ginkgo biloba. Here a MADS-box transcription factor gene, designated as GbMADS9, was cloned and functionally characterized from G. biloba. The open reading frame of GbMADS9 comprised 684 bp encoding a polypeptide of 227 amino acids. Phylogenetic analysis showed that GbMADS9 belonged to the GGM13 clade of Bsister-class MADS-box proteins. Real-time PCR results revealed that GbMADS9 was preferentially expressed in strobili and ovules. In addition, its expression was up-regulated with the increase in the size of ginkgo pulp, indicating that GbMADS9 had a positive function in ginkgo ovule development. The expression of GbMADS9 in ginkgo was up-regulated in response to salinity, drought, and cold stress, as well as to phytohormones gibberellic acid and abscisic acid. GbMADS9 transgenic Arabidopsis plants presented early flowering phenotypes compared with wild-type plants. The expression of the FLOWERING LOCUS T (FT), APETALA1 (AP1), LEAFY (LFY), and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) genes involved in flowering was up-regulated, whereas the expression of AGAMOUS-LIKE24 (AGL24) and SHORT VEGETATIVE PHASE (SVP) was down-regulated in the GbMADS9 transgenic lines. The GbMADS9 transgenic plants exhibited better growth than wild-type plants under high osmotic stress. Enhanced tolerance of transgenic Arabidopsis plants to osmotic stress was confirmed by changes in the chlorophyll, proline, and malondialdehyde contents. Moreover, increased tolerance to osmotic stress in GbMADS9 transgenic lines was associated with improved antioxidant enzymatic activities. These findings suggested that GbMADS9 might be a promising gene to manipulate flowering time and improve abiotic stress tolerance in G. biloba.