Transcriptomic and metabolomic analyses unveil the growth advantage mechanism conferred by heterosis of Michelia 'Zhongshanhanxiao'.

Michelia compressa (Maxim.) Sarg. is one of the important timber trees in Taiwan province, P. R. China. Michelia 'Zhongshanhanxiao' is a group of variants found among the progeny of M. compressa that exhibit higher growth rates compared with normal individuals, with significantly increased stem diameter and height, as well as enlarged leaves and flowers. However, the molecular mechanisms fostering the growth advantage and morphological variations are unknown and deserve further study. Through analyzing the transcriptome, metabolome and physiological processes of leaves, we identified remarkable differences in gene expression and metabolic profiles between Michelia 'Zhongshanhanxiao' and both the maternal M. compressa and its normal progeny. These differences were widely associated with plant-pathogen interaction, phenylpropanoid biosynthesis, cyanoamino acid metabolism, carbon fixation in photosynthetic organisms and plant hormone signal transduction. Additionally, physiological measurements showed that Michelia 'Zhongshanhanxiao' possesses stronger photosynthetic capacity and higher plant hormone contents. These results suggest that the heterosis of Michelia 'Zhongshanhanxiao' is regulated by candidates related to cell division, resistance to pathogens and accumulation of organic compounds. The findings of this study provide crucial information on the molecular mechanisms underlying the growth advantages conferred by heterosis in trees.