Fig. 1

Morphological characteristics, oil accumulation and temperature variation in the process of hickory embryo development. The solid and the dashed red lines indicate the curves of oil content during the embryo development in 2012 and 2013, respectively. And, the solid and the dashed blue lines indicate the curves of top atmosphere temperature with the embryo development in two years, respectively. DAP indicates day after pollination. S1-S5 or T1-T5 indicate 5 temporal developmental stages, i.e., early cotyledon stage, midcotyledon stage, late cotyledon stage, full cotyledon stage, and maturation stage in 2012 and 2013 respectively, and chosen for RNA-seq analysis