Hypothesised molecular model of flowering in C. pallens
This study showed a strong conservation of the activity of PEBP-like gene family members as floral promoters in C. pallens . Transcriptomic analysis further suggested that C. pallensundergoes flowering through the interaction of external and internal signals which can be integrated at the CpATFL1 loci to initiate flowering.
We suggest that flowering in the masting plant C. pallens is a coordinated two-step process (Fig. 5). In the first stage, winters may suppress the activity of CpVRN2 by increasing the expression ofCpVRN1 , thereby elevating the expression of FT -like genes in the spring, each year. However, an increase in the FTs does not necessarily correlate with flowering in plants in the next season. In the second stage, only plants with sufficient internal cues and consequently a greater expression of CpATFL1 may be able to respond to the floral transition and, subsequently, flower. This two-stage process almost certainly requires additional epigenetic factors acting on CpATFL1 to control the reproductive transition. Further analysis based on CHiP-seq may allow the identification of the specific epigenetic genes and the corresponding methylation changes in the histones to activate the flowering process in response to the environmental cues.
Because of the potential impacts of global climate change on masting phenology (Monks et al., 2016), and the potential down-stream impacts on introduced and native fauna (Griffiths & Barron, 2016), it is becoming increasingly important to accurately predict masting years. Such predictions are strongest when they are based on a detailed mechanistic understanding of the underlying control mechanisms. The current study has identified significant molecular regulators of flowering in C. pallens which can be used to explore changes in flowering gene expression under altered climates. This will allow the design of new masting models with greater confidence and to understand how mast flowering may change in the face of climate change.