AUTHOR=Du Wei , Ding Jian , Li Jingbin , Li He , Ruan Chengjiang 

TITLE=Co-regulatory effects of hormone and mRNA–miRNA module on flower bud formation of Camellia oleifera

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 14 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1109603

DOI=10.3389/fpls.2023.1109603

ISSN=1664-462X

ABSTRACT=The few flower buds in a high-yield year are the main factors restricting the yield of Camellia oleifera in the next year. However, there are no relevant reports on the regulation mechanism of flower bud formation. In this study, hormones, mRNAs and miRNAs were tested during flower bud formation in MY3 (“Min Yu 3” with stable yield in different years) and QY2 (“Qian Yu 2”, less flower bud formation in high-yield year) cultivars. The results showed that except for IAA, hormone contents GA3, ABA, tZ, JA and SA in the buds were higher than those in the fruit, and the contents of all hormones in the buds were higher than those in the adjacent tissues. This excluded the effect of hormones produced from the fruit on flower bud formation. The difference in hormone showed that April 21-30 was the critical period of flower bud formation of C. oleifera, the JA content in MY3 was higher than that in QY2, but lower concentration of GA3 contributed to the formation of C. oleifera flower bud. JA and GA3 might have different effects on flower bud formation. Comprehensive analysis of the RNA-seq data showed that differentially expressed genes were notably enriched in hormone signal transduction and the circadian system. Flower bud formation of MY3 was induced through the plant hormone receptor TIR1 (transport inhibitor response 1) of the IAA signaling pathway, miR535-GID1c  module of the GA signaling pathway, and miR395-JAZ module of the JA signaling pathway. In addition, the expression of core clock component GI (GIGANTEA) and CO (CONSTANS) in MY3 increased 2.3-fold and 1.8-fold over that in QY2, respectively, indicating that the circadian system also played a role in promoting flower bud formation in MY3. Finally, the hormone signaling pathway and circadian system transmitted flowering signals to the floral meristem characteristic genes LFY (LEAFY) and AP1 (APETALA 1) via FT (FLOWERING LOCUS T) and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) to regulate flower bud formation. These data will provide the basis for understanding the mechanism of flower bud alternate formation and formulating high yield regulation measures of C. oleifera.