Control of masting may be epigenetic

Masting, when perennial plants all flower at the same time but at irregular annual intervals, results in a very high seed set some years and little to none in others. The phenomenon occurs in 37 different plant families and occurs primarily in long-lived woody and wind-pollinated species. Masting keeps seed-eating herbivores overwhelmed with food during mast years, bettering survival for seeds overall, while decreasing the herbivores’ populations through starvation other years. The phenomenon is well-understood ecologically, but poorly understood at the molecular level.

In a recent viewpoint published in Annals of Botany, author Samarth and colleagues discuss ecological temperature models to predict masting and introduce the concept of ‘epigenetic summer memory’ as a mechanism of mast-year timing. Mast years are known to follow warm temperatures in previous growing seasons, but rather than merely accounting for the previous single year’s temperatures, a better predictive fit seems to come from looking at the increase in temperature over the two years prior to the mast year. It is not known for certain either how the plants ‘remember’ the conditions of the prior two years, or the molecular mechanism that triggers masting, but the authors suggest that the answer may lie in epigenetic marking.

“[W]e suggest it is the balance between activating epigenetic marks and repressive epigenetic marks on both promoters and repressors of flowering in response to the summer temperatures over two years which determines mast flowering. This molecular network, being common across many species, where activation of floral integrator genes subsequently activates the floral meristem genes to initiate the floral transition, could provide for the strong synchrony of flowering observed during mast flowering years,” they write. The epigenetic summer memory concept theorizes that temperature changes affect methylation patterns in flowering genes, and that two successive years of this activation are needed to reach a commitment point for the meristem.

With the global temperature increasing and temperature patterns becoming increasingly erratic, researchers are uncertain about the overall effect on masting, and what the downstream effect on seed predation will be. The authors encourage further work on the molecular basis of masting. “Molecular studies have the potential to be used to forecast changes in flowering behaviour and to provide an understanding of how changes in natural conditions may lead to adaptation of flowering time genes under a changing global climate. To gain a better understanding of the mechanisms underpinning masting requires a critical evaluation and analysis of the molecular flowering pathway operational in masting plants,” they write.