Pollen priming for more efficient reproduction in a heating world: what we know, what we need to know

Global warming is predicted to alter temperatures thereby leading to a significant loss in crop productivity and yield. One target of global warming is plant sexual reproduction, which will be deeply threatened by high temperatures because the male gametophyte (the pollen) is particularly susceptible to heat stress. As a reaction to the latter, pollen enacts many responses that involve specific reprogramming of genetic, metabolic, and cellular activities. Most published works focus on a single episode of heat stress but less is known about the effects of heat pre-exposure (priming) on acquired thermotolerance (ATT). The purpose of this review is to gain a deeper understanding of ATT mechanisms in pollen and pollen tube, primarily from available literature. In particular, we will examine many facets (cell wall, cytoskeleton, ion fluxes, reactive oxygen species, etc.) that could be both targets of heat stress and active responses to priming.