Transcriptome and widely metabolomic analysis reveal hormones and sugar signaling pathways contribute to the normal growth of seeds in young Picea neoveitchii Mast. trees

Abnormal seed growth is a problem in Picea neoveitchii Mast. in China that threatens the existence of this evergreen coniferous tree. However, the degree of abnormal seed growth varies in different age groups; regrettably, the causes behind abnormal seed growth at different ages are totally unclear. Thus, we compared the seeds of two ages: Gansu (GS) province, a 50-year-old tree (GS50), and a 300-year-old tree (GS300). Results indicated that 22187 unigenes were commonly found in both groups, whereas 5328 and 6079 unigenes were uniquely found in GS50 and GS300, respectively. Furthermore, a total of 5129 differentially expressed unigenes were identified between GS50 and GS300, with 2431 upregulated and 2698 downregulated. On the basis of Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, plant hormone signal transduction and starch and sucrose metabolism pathways were further selected for their potential involvement in seed growth at both ages. A wide-targeted metabolomics-based approach using liquid chromatography mass spectrometry (LC-MS) was applied to study the difference between GS50 and GS300. The results showed that there were 35 different metabolites in total being detected, mainly amino acids and sugars. Subsequently, GS50 revealed the highest number of normal seeds and the lowest number of abnormal seeds in comparison with GS300 by improving endogenous indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellic acid 3 (GA₃) contents and reducing methyl jasmonate (JA-me), abscisic acid (ABA), and brassinosteroid (BR) contents. Our research provides important evidence on the growth of seeds in different age groups of trees that might help improve seed growth in old trees.