Objective The dynamic changes of seed contents and transcriptome analysis of Photinia bodinieri and P. atropurpurea during germination were studied to explore the developmental mechanisms involved in the germination of the two seeds, and to provide references for the selection and development of new varieties.

Methods Seeds from both varieties were analyzed for nutrient content and endogenous hormone levels during germination. High-throughput sequencing technology using Illumina NovaSeq6000 was employed for transcriptome sequencing at the seed growth stage of P. bodinieri and P. atropurpurea.

Results 1)The germination mode of the two kinds of photinia seeds was cotyledone-unearthed type. During the germination process, the germination rate of P.bodinieri seeds was higher than that of P. atropurpurea. 2)In the dry seed state, the reducing sugar content of P.bodinieri was higher than that of P. atropurpurea. In the process of germination, the change trend of nutrients of the two species was basically the same, but in general, the nutrient content of P. bodinieri was always higher than that of P. atropurpurea. In addition, at the dry seed stage, the ABA content of P. atropurpurea was higher than that of P. bodinieri, while the GA3, IAA and MEIAA contents of P. bodinieri were higher than that of P. atropurpurea. During the whole germination process, the IAA content of both sides decreased, while the ratio of GA3/ABA to IAA/ABA increased first and then decreased. 3) A total of 186 810 unigenes were obtained through transcriptome sequencing. Among these unigenes, 157 309 received annotations across seven functional databases with approximately 67.94% annotated within Rosaceae family-related categories. GO enrichment analysis indicated that lignin metabolism along with oxidoreductase activity played significant roles during seed germination processes. However, in terms of cell composition, photosynthesis showed significant enrichment only in P. bodinieri. The results of KEGG enrichment showed that metabolic pathways related to ribosome, plant hormone signaling and MAPK signaling pathways were active during the germination of the two seeds. Compared with P. atropurpurea , P. bodinieri had more genes regulating metabolic pathways and more active genes regulating seedling development during the whole growth and development. In addition, multi-family transcription factors such as C3H, AP2, bZIP and MYB were expressed in large quantities in the germination physiology of the two types of Photinea seeds.

Conclusion According to the dynamic changes of contents during seed germination of P. bodinieri and P. atropurpurea and transcriptome sequencing results, due to the differences in the expression of related genes, regulation of plant hormone signal, MAPK signal, photosynthesis and other metabolic activities related to seed germination, the growth potential of P. bodinieri was better than that of P. atropurpurea at seedling stage. The changes of contents and transcriptome levels indicated that the seeds of P. bodinieri might release dormancy and start germination faster than that of P. atropurpurea.