Deciphering the effect mechanism of chromosome doubling on the biomass increase in Elsholtzia splendens

Elsholtzia splendens is an ideal plant species for remediating copper-contaminated soils. However, its application range is regrettably hindered by its generally low biomass and rather narrow range of suitable growing conditions. Polyploid technique is a shortcut to enhance biomass and environmental adaptability of plant, which may become an important breakthrough to improve application value of E. splendens. In this study, tetraploid E. splendens (2n = 4x = 32) was successfully obtained from wild E. splendens (2n = 2x = 16) using a primary meristem processing technique for the first time, exhibiting a huge biomass advantage. In order to find out the underlying mechanism for its huge biomass advantage, a series of difference assessments between two ploidy-level E. splendens were performed, including morphological, anatomical, physiological, photosynthesis, transcriptome and endogenous hormones experiments. All the results consistently showed that enhanced photosynthesis and alterated cell differentiation function drove significant biomass increase. During the process of excavating molecular mechanism deeply, five hub genes (regulating Rubisco, light-harvesting chlorophyII a/b-binding protein 2 (Lhcb2), photosystem I subunit PsaO (PsaO), magnesium protoporphyrin IX methyltransferase (ChlM) and lateral organ boundaries (LOB) domain (LBD)) were found to play extremely vital roles in biomass increase regulation. Especially, LOB may be the most key factor resulting in the transformation of E. splendens from a single plant to a cluster, ultimately leading to biomass multiplication. Finally, a responsive model was proposed to elucidate the regulatory mechanisms of huge biomass in the tetraploid E. splendens. The present findings provide new evidence for understanding the complex regulatory networks responsible for remarkable biomass increase in polyploid plants.