Molecular Cloning and Functional Characterization of the DELLA Gene Family in Liriodendron Hybrids

Abstract

DELLA proteins are key components of the gibberellins signal transduction pathway that play negative roles on promoting cell elongation and plant stature. However, the mechanisms underlying DELLA mediated growth inhibition in woody plant species are poorly understood. Here, we identified two LhDELLA genes including LhSLR-like (LhSLRL) and LhRGA from Liriodendron hybrids (Liriodendron chinense (Hemsl.) Sarg. × L. tulipifera L.), which is a horticultural tree with high-quality timber. Sequence analysis showed that LhSLRL and LhRGA possessed all typical conserved domains of DELLA proteins. Phylogenetic analysis showed that LhRGA was classified as the basal branch of DELLAs from species belonging to dicots. Interestingly, LhSLRL was a sister clade of DELLAs from the most ancient plant species such as bryophytes and ferns. Gene expression analysis showed that LhSLRL and LhRGA genes had the highest expression level in the stem. In addition, overexpression of LhSLRL decreased plant height and root length, increased branching and delayed flowering in Arabidopsis thaliana, while LhRGA overexpression enlarged leaves and reduced the number and length of roots. Overexpressing LhSLRL in tobacco caused a decreased plant height and the amount of root. Taken together, these results reveal that LhDELLA genes may play an important role in plant growth and development, especially in vegetative organs. Our results provide new insights into the function of DELLA genes in a woody plant, and contribute to a potential application of manipulating DELLA genetics.