Cryptic isoprene emission of soybeans under wounding and high temperature

Isoprene is the most abundant non-methane biogenic hydrocarbon emitted by
some plants, mostly trees. It plays a critical role in atmospheric
chemistry by contributing to ozone and aerosol formation. Isoprene also
benefits plants, particularly under stress, through its signaling roles.
Legume crops like soybean were thought to have evolutionarily lost
isoprene synthase (ISPS) and are typically considered non-emitters. Here
we report that damage to soybean leaves by wounding or burning triggered a
burst of isoprene emission from undamaged parts of the leaves. In
silico analysis identified intact ISPS genes in the soybean
genome, with features similar to known ISPSs. Protein made from these gene
sequences catalyzed isoprene production in the presence of dimethylallyl
diphosphate. Isoprene emission in soybeans was linked to reduced
photosynthesis rates and stomatal conductance. Metabolomic analysis showed
that leaf damage caused a surge in glyceraldehyde 3-phosphate and pyruvate
levels, leading to an increase of most of the methylerythritol 4-phosphate
(MEP) pathway metabolites. Heat stress also led to significant isoprene
emission from soybean leaves. We conclude that soybeans possess functional
ISPSs and can make isoprene only under some conditions by regulating
photosynthesis and MEP pathway.