Genome-wide analysis of physic nut MADS-box gene family and functional characterization of the JcMADS05 gene in transgenic rice

Background: Physic nut (Jatropha curcas), a non-edible oilseed plant, is among the most promising alternative energy sources because of its high seed oil content, rapid growth and extensive adaptability. Proteins encoded by MADS-box genes are important transcription factors involved in the regulation of plant growth, seed development and responses to abiotic stress. However, there has been no in-depth research on the MADS-box genes and their roles in physic nut. Results: In the present study, 63 MADS-box genes (JcMADSs) were identified in the physic nut genome, and classed into five groups (MIKC, Mα, Mβ, Mγ, Mδ) based on phylogenetic comparison with Arabidopsis homologs. Expression profile analysis based on RNA-seq suggested that many JcMADS genes were expressed most strongly in seeds, and seven of them responded in leaves to at least one abiotic stressor (drought and/or salinity) at one or more time points. Transient expression analysis and a transactivation assay indicated that JcMADS05 is a nucleus-localized transcriptional activator. Plants overexpressing JcMADS05 did not show altered plant growth, but the overexpressing plants did exhibit reductions in grain size, grain length, grain width, 1000-seed weight and yield per plant. Further data on the reduced grain size in JcMADS05-overexpressing plants supported the putative role of JcMADS genes in seed development. Conclusions: This study will be useful in understanding the involvement of MADS-box genes in growth and development in addition to their functions in abiotic stress resistance, and will ultimately form the basis for functional characterization and the exploitation of candidate genes for the genetic engineering of physic nut.