State Key Laboratory of Crop Genetics and Germplasm Enhancement and Utilisation, Key Laboratory of Landscaping, Ministry of Agriculture and Rural Affairs, Key Laboratory of Biology of Ornamental Plants in East China, National Forestry and Grassland Administration, Zhongshan Biological Breeding Laboratory, College of Horticulture, Nanjing Agricultural University, Nanjing, China.
Plant Cell Environ. 2024 Aug;47(8):2923-2935. doi: 10.1111/pce.14919. Epub 2024 Apr 17.
Floral transition, the switch from vegetative to reproductive growth, is extremely important for the growth and development of flowering plants. In the summer chrysanthemum, CmBBX8, a member of the subgroup II B-box (BBX) family, positively regulates the transition by physically interacting with CmERF3 to inhibit CmFTL1 expression. In this study, we show that CmBBX5, a B-box subgroup I member comprising two B-boxes and a CCT domain, interacts with CmBBX8. This interaction suppresses the recruitment of CmBBX8 to the CmFTL1 locus without affecting its transcriptional activation activity. CmBBX5 overexpression led to delayed flowering under both LD (long-day) and SD (short-day) conditions, while lines expressing the chimeric repressor gene-silencing (CmBBX5-SRDX) exhibited the opposite phenotype. Subsequent genetic evidence indicated that in regulating flowering, CmBBX5 is partially dependent on CmBBX8. Moreover, during the vegetative growth period, levels of CmBBX5 expression were found to exceed those of CmBBX8. Collectively, our findings indicate that both CmERF3 and CmBBX5 interact with CmBBX8 to dampen the regulation of CmFTL1 via distinct mechanisms, which contribute to preventing the premature flowering of summer chrysanthemum.
花发育转变，即从营养生长向生殖生长的转变，对开花植物的生长和发育极为重要。在夏菊中，CmBBX8，一个 II B-box 亚组（BBX）家族的成员，通过与 CmERF3 物理相互作用抑制 CmFTL1 的表达来正向调控这一转变。在本研究中，我们发现 CmBBX5，一个包含两个 B-box 和一个 CCT 结构域的 I 亚组 BBX 成员，与 CmBBX8 相互作用。这种相互作用抑制了 CmBBX8 招募到 CmFTL1 基因座，而不影响其转录激活活性。CmBBX5 的过表达导致 LD（长日）和 SD（短日）条件下开花时间延迟，而表达嵌合抑制基因沉默（CmBBX5-SRDX）的株系则表现出相反的表型。随后的遗传证据表明，在调控开花时间方面，CmBBX5 部分依赖于 CmBBX8。此外，在营养生长期间，CmBBX5 的表达水平被发现超过了 CmBBX8。总的来说，我们的研究结果表明，CmERF3 和 CmBBX5 都与 CmBBX8 相互作用，通过不同的机制来抑制 CmFTL1 的调节，这有助于防止夏菊过早开花。
