Seasonal gene-expression signatures of delayed fertilization in Fagaceae

Abstract

In the family Fagaceae, fertilization is delayed by several weeks to one year after pollination, leading to one- or two-year fruiting species depending on whether fruiting occurs in the same or the next year after flowering. To investigate physiological responses underlying the regulation of delayed fertilization, we monitored seasonal changes in genome-wide gene expression in tissues including leaves and buds over two years under natural conditions in one- (Quercus glauca) and two-year fruiting species (Lithocarpus edulis). Genes associated with the responses to cold stress, photosynthesis, and cell proliferation, which are essential for survival and growth, showed highly conserved seasonal expression profiles regardless of species. However, seasonal expression profiles diverged between the one- and two-year fruiting species in genes associated with pollination, an important process contributing to the origin and maintenance of the reproductive barrier between plant species. By comparing seasonal progression of ovule development and gene expression in pistillate flowers, we revealed that ovules started developing after winter in the two-year fruiting species, which could be linked to the activation of genes involved in fertilization and female gametophyte development after winter. These findings suggest that the two-year fruiting species may have evolved a requirement of winter cold to prevent fertilization before winter and facilitate fertilization and embryo development in the following spring when temperature rises. This study offers new possibilities to explore the evolution of reproductive strategies in Fagaceae.

Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC

“…In a similar manner, when the effectiveness of the isoprene 𝑏(𝑡) drops in midsummer due to the high volatility, the optimal isoprene production has a peak in spring. These are not the pattern observed for genes involved in the pathway for production of isoprene [18]. Hence, we may conclude that the simplest way to explain the peak isoprene production in the midsummer is the high heat stress.…”

“…The amount of isoprene production by trees is very large [2], and BVOCs may modify the local and global climates [3], [4], [39]. Studies of the molecular and physiological mechanisms have also been advanced [40], [41], [42], [43], [44], [45], [18]. Understanding the seasonal pattern of gene expression would be helpful in revealing the mechanism controlling genes, considering the respective roles of their products.…”

“…In a study of genome-wide gene expression data, focusing on Quercus glauca and Lithocarpus edulis in warm temperate regions of Japanese islands, genes related to sesquiterpene production were highly expressed in spring, while genes related to isoprene production exhibited high expression in the middle of the summer 18,19 . Sesquiterpene is much less volatile than isoprene.…”

“…For example, both Quercus glauca and Lithocarpus edulis are trees of the Fagaceae family living in warm temperate regions of the Japanese islands. In both species, the genes related to isoprene production show high expression in the middle of the summer [18], [19]. The gene expression does not necessarily imply the production of respective chemicals, as it is often subject to additional regulatory processes.…”