pre-mRNA splicing regulates cellular dedifferentiation via lipid metabolism in a cytokinin-dependent manner in Arabidopsis
Plant cells have a high plasticity of proliferation and differentiation, and the importance of pre-mRNA splicing for such cell plasticity was previously revealed. Here, we report the responsible gene for root redifferentiation defective4-1 (rrd4-1), a high temperature-sensitive Arabidopsis mutant for callus formation from hypocotyls, is also involved pre-mRNA splicing. Interestingly, the inhibition of callus formation in rrd4-1 at 28Â°C was dependent on kinetin, a kind of cytokinin, in callus-inducing medium. RNA-seq analysis demonstrated that the genes for secondary cell wall biogenesis and cell cycle progression are up- and down-regulated in rrd4-1 at 28Â°C, respectively, in the cytokinin-dependent manner, as reflecting no resumption of cell division in rrd4-1. Moreover, kinetin and rrd4-1 mutation affected alternative splicing broadly; especially, the genes for sphingolipid metabolism (PTPLA, SPHK2, ATNCER1) were affected by both of kinetin and rrd4-1 mutation. Indeed, very-long-chain (VLC) sphingolipids were continuously decreased in rrd4-1, and callus induction with kinetin changes the contents of ceramide with VLC fatty acids. Kinetin enhanced the inhibitory effect of cerulenin (a lipid synthesis inhibitor) on callus formation, and rrd4-1 was hypersensitive to cerulenin. Taken together, our data suggest that pre-mRNA splicing modulates cytokinin-mediated cellular dedifferentiation, through the alternative splicing of lipid metabolism genes.