Auxin regulates bulbil initiation by mediating sucrose metabolism in Lilium lancifolium

Abstract

Lily bulbils, which serve as advantageous axillary organs for vegetative propagation, have not been extensively studied in terms of the mechanism of bulbil initiation. The functions of auxin and sucrose metabolism have been implicated in axillary organ development, but their relationship in regulating bulbil initiation remains unclear. In this study, exogenous indole-3-acetic acid (IAA) treatment increased the endogenous auxin levels at leaf axils and significantly decreased bulbil number, whereas treatment with the auxin polar transport inhibitor N-1-naphthylphthalamic acid (NPA), which resulted in a low auxin concentration at leaf axils, stimulated bulbil initiation and increased bulbil number. A low level of auxin caused by NPA spraying or silencing of auxin biosynthesis genes YUCCA FLAVIN MONOOXYGENASE-LIKE 6 (LlYUC6) and TRYPTOPHAN AMINOTRANSFERASE RELATED 1 (LlTAR1) facilitated sucrose metabolism by activating the expression of SUCROSE SYNTHASES 1 (LlSusy1) and CELL WALL INVERTASE 2 (LlCWIN2), resulting in enhanced bulbil initiation. Silencing LlSusy1 or LlCWIN2 hindered bulbil initiation. Moreover, the transcription factor BASIC HELIX-LOOP-HELIX 35 (LlbHLH35) directly bound the promoter of LlSusy1, but not the promoter of LlCWIN2, and activated its transcription in response to the auxin content, bridging the gap between auxin and sucrose metabolism. In conclusion, our results reveal that an LlbHLH35-LlSusy1 module mediates auxin-regulated sucrose metabolism during bulbil initiation.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 32371954 and 32171864 to Y.D.; 32372740 and 32172617 to J.W.; 32302599 to J.L.), the Excellent Youth Science Foundation of Beijing Academy of Agriculture and Forestry Sciences (YXQN202303 to Y.D.), Pinduoduo-China Agricultural University Research Fund (PC2023B02009), Construction of Beijing Science and Technology Innovation and Service Capacity in Top Subjects (CEFF-PXM 2019_014207_000032), and the 2115 Talent Development Program of China Agricultural University, the Strategic Development Department of China Association for Science and Technology, 111 Project of the Ministry of Education (B17043), and China Postdoctoral Science Foundation (2023M740311).

Author contributions

X.C. and Y.X. observed the development of bulbil and performed the endogenous hormone treatments; Y.X. and W.P. conducted the transcriptome analysis; X.C., Y.X., and S.W. performed gene silencing; Y.X., J.X.W., and M.F.Z. conducted the metabolite analysis; X.C., Y.X., J.L, J.W., and M.Z. wrote and rewrote the article; J.W., Y.D., X.Y., X.C., J.L., and X.Z. conceived the study and reviewed the article; all authors read and approved the article.

Data availability statement

The raw sequence data of RNA-seq reported in this study have been deposited in the NCBI SRA data under accession number PRJNA916842. The authors declare that all data supporting the findings of this study are available from within the article and supplementary data or are available upon reasonable request from the corresponding author.

Conflict of interest

The authors report no declarations of interest.

Supplementary data

Supplementary data are available at Horticulture Research online.

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