miRNA regulation contributes to increased photosynthetic capacity in auto tetraploids pak choi

Polyploid plants generally demonstrate enhanced photosynthetic capacity compared to their diploid ancestors; however, the mechanisms underlying this phenomenon remain largely unexplored. This study utilizes pak choi [Brassica campestris (syn. Brassica rapa) ssp. chinensis] as the material to investigate the molecular mechanisms underlying enhanced photosynthesis in autotetraploid. Our findings indicate that autotetraploid pak choi leaves exhibit increased thickness, enlarged intercellular spaces, and cell dimensions, as well as augmented accumulation of thylakoids and grana. Photosynthesis data indicate that the net photosynthesis (Pn) of autotetraploid plants is significantly greater than that of diploid plants. Transcriptome and miRNA sequencing revealed that the differentially expressed genes were significantly enriched in the photosynthesis thylakoid pathway. Joint analysis revealed that novel-miRNA117 regulates BcLhcb1 and BcLhcb4.2, whereas Bc-miR403-5p regulates BcLhcb4.2. The downregulation of BcLhcb1, BcLhcb2.1, and BcLhcb4.2 resulted in reduced Pn in pak choi, whereas their overexpression increased the growth of Arabidopsis and increased plant weight, which was attributed to the tight stacking of thylakoid granules in the overexpressing plants. Additionally, we observed weakened growth in Arabidopsis overexpressing novel-miRNA117 and Bc-miR403-5p, which was consistent with the phenotype resulting from the silencing of BcLhcbs. These findings further demonstrated that miRNA117 regulates BcLhcb1 and BcLhcb4.2, whereas Bc-miR403-5p regulates BcLhcb2.1. This study enhances our understanding of the molecular mechanisms underlying photosynthesis in homogenous autotetraploid pak choi. Furthermore, it provides novel insights into the regulatory roles of miRNAs in polyploid photosynthesis and contributes to the molecular breeding of pak choi.