Populus tremula x Populus alba Raw sequence reads

Isoprene (C5H8), the most abundant biogenic volatile hydrocarbon in the atmosphere, is constitutively released by the leaves of some of the fastest-growing and most speciose forest trees1. While isoprene influences global climate, it also serves emitting plants by mitigating heat and oxidative stresses. However, we do not understand why isoprene emission is constitutive and not merely stress-induced. Using Arabidopsis genetically transformed to emit isoprene, and naturally isoprene-emitting poplar trees where isoprene biosynthesis was suppressed, here we show that the ability to emit isoprene significantly enhances the abundance of leaf cytokinins (CKs), a group of vital growth hormones regulating plant development and senescence. Genes regulating CK-synthesis, CK-signaling and CK-degradation are significantly overexpressed in isoprene-emitting leaves. By priming leaf CK-metabolism, isoprene emission accelerates plant growth, affects chloroplast metabolic rate and leaf energy status, induces early leaf senescence, and shortens plant generation time. The results unveil a hitherto unknown evolutionary and house-keeping function for constitutive isoprene emission in shaping plant life-history strategies.