Hickory (Carya cathayensis Sarg.) is an extraordinary nut-bearing deciduous arbor with high content of oil in its embryo. However, the molecular mechanism underlying high oil accumulation is mostly unknown. Here, we reported that the lipid droplets and oil accumulation gradually increased with the embryo development and the oil content was up to ~76% at maturity. Furthermore, transcriptome and proteome analysis of developing hickory embryo identified 32,907 genes and 9857 proteins. Time-series analysis of gene expressions showed that these genes were divided into 12 clusters and lipid metabolism-related genes were enriched in Cluster 3, with the highest expression levels at 95 days after pollination (S2). Differentially expressed genes and proteins indicated high correlation, and both were enriched in the lipid metabolism. Notably, the genes involved in biosynthesis, transport of fatty acid/lipid and lipid droplets formation had high expression levels at S2, while the expression levels of other genes required for suberin/wax/cutin biosynthesis and lipid degradation were very low at all the sampling time points, ultimately promoting the accumulation of oil. Quantitative reverse-transcription PCR analysis also verified the results of RNA-seq. The co-regulatory networks of lipid metabolism were further constructed and WRINKLED1 (WRI1) was a core transcriptional factor located in the nucleus. Of note, CcWRI1A/B could directly activate the expression of some genes (CcBCCP2A, CcBCCP2B, CcFATA and CcFAD3) required for fatty acid synthesis. These results provided in-depth evidence for revealing the molecular mechanism of high oil accumulation in hickory embryo.

Hickory (Carya cathayensis) is a critical tree species of the genus Carya from the Juglandaceae family that contains nutrient-rich nuts. Due to large-scale soil degradation, the pests and diseases of hickory are becoming more and more serious. Thaumatin-like proteins (TLPs) are vital proteins involved in the complex defense process of plant pathogens. In this study, 40 CcTLP genes were identified genome-widely and phylogenetically grouped into three subfamilies. The sequence of CcTLPs had a conservative pattern, such as eight stable disulfide bonds, REDDD, and G-X-[GF]-X-C-X-T-[GA]-D-C-X(1,2)-G-X-(2,3)-C structure. In total, 57 cis-elements related to stress-responsive, light-responsive, phytohormone-responsive, and plant-responsive were discovered. Under salicylate (SA), methyl jasmonate (MeJA), and ethephon (ETH) treatments, the expressions of CcTLP28, CcTLP29, CcTLP30, CcTLP31, CcTLP32, CcTLP33, CcTLP37, CcTLP38, and CcTLP39 had different patterns. This is an indication that most of the TLP genes were upregulated by SA and downregulated by MeJA. Notably, seven TLP genes were significantly upregulated under the Botryosphaeria dothidea inoculation, especially CcTLP31, with an over 20-fold change. Nine genes were shown by subcellular localization analysis to be located at the plasma membrane and cytoplasm. The knowledge of the disease-resistant function of the CcTLP family in hickory is promoted by these results. A foundation reference for the molecular breeding of this plant in the future is provided by our findings.

Targeted regulation using transgrafting technology has become a trend. However, the mechanisms of transgene-derived signal communication between rootstocks and scions remain unclear in woody plants. Here, we grafted wild-type (WT) walnut (Juglans regia L.) on WT (WT/WT), JrGA20ox1 (encodes a gibberellin 20-oxidase)-overexpressing (WT/OE), and JrGA20ox1-RNAi transformation (WT/RNAi) walnut in vitro. We aimed to elucidate the mechanisms of JrGA20ox1-derived signal communication under PEG-simulated drought stress between rootstocks and scions in walnut. We demonstrated that JrGA20ox1-OE and JrGA20ox1-RNAi rootstocks could transport active gibberellins (GAs) and JrGA20ox1-RNAi vector-produced sRNAs to WT scions under PEG-simulated drought stress, respectively. The movement of sRNAs further led to a successive decline in JrGA20ox1 expression and active GA content. Meanwhile, unknown mobile signals may move between rootstocks and scions. These mobile signals reduced the expression of a series of GA-responsive and GA-non-responsive genes, and induced ROS production in guard cells and an increase in ABA content, which may contribute to the drought tolerance of WT/RNAi, while the opposite occurred in WT/OE. The findings suggest that JrGA20ox1-derived rootstock-to-scion movement of signals is involved in drought tolerance of scions. Our research will provide a feasible approach for studying signal communication in woody plants.