Roots of abundance: Unraveling the auxin-sucrose nexus in Lily bulbil formation
image: Morphological and histological observation of bulbil development. A Phenotypes of bulbil development in leaf axils from the first day of planting and continuing for 60 days. All white scale bars represent 1 cm. B Histological observations of bulbil formation. (i)–(iii) Epidermis cells of leaf axils underwent anticlinal and periclinal division, referred to as the ‘No bulbil’ stage. (iv) Apparent convexity appeared on the leaf axil, referred to as the ‘White dot’ stage. (v)–(vi) White bulbil dots further developed into mature bulbils with scales. All black scale bars represent 200 μm. AM, axillary meristem; LA, leaf axil; LP, leaf petiole; MS, main stem; SAM, shoot apical meristem; SC, scale. C, D Diagrammatic representation showing the distribution of bulbils in 30 independent plants on day 60 after planting: growth stages of bulbils (C) and number of bulbils per leaf axil (D). Each column represents a plant, and each box represents the type of bulbil. L1 represents the first leaf axil of the plant, and L means ‘leaf axil’. E Proportion of number of bulbils per leaf axil. Thirty biological replicates were performed. F, G Correlation between number of bulbils and plant height (F) and correlation between number of bulbils and number of leaves (G). Thirty biological replicates were performed. Pearson’s correlation (r) analyses (P<0.05) and scatter plots show the data distribution.
Credit: Horticulture Research
A pivotal study reveals how auxin and sucrose metabolism regulate bulbil initiation in Lilium lancifolium. By manipulating auxin levels and examining key sucrose metabolism genes, researchers found that low auxin concentrations enhance bulbil formation. This discovery offers promising implications for horticulture, providing new strategies to improve bulb propagation through hormonal and metabolic pathways.
Bulbils in lilies serve as crucial vegetative reproductive organs, ensuring plant survival and propagation. The initiation of these structures, however, is not well-understood, particularly the roles of hormonal and metabolic pathways. Auxin, a plant hormone, is known to regulate various growth processes, including lateral organ formation. Sucrose metabolism provides essential energy and substrates for plant development. Despite these known functions, the interplay between auxin and sucrose metabolism in bulbil initiation remains unclear. Based on these challenges, it is necessary to conduct in-depth research to understand the mechanisms underlying bulbil initiation.
Researchers from the Beijing Academy of Agriculture and Forestry Sciences and China Agricultural University published a study (DOI: 10.1093/hr/uhae054) in Horticulture Research on February 23, 2024, revealing the mechanisms by which auxin regulates bulbil initiation in Lilium lancifolium. The study investigates how auxin levels, manipulated through treatments and gene silencing, affect sucrose metabolism and subsequently bulbil formation.
The study focused on understanding the role of auxin in bulbil initiation in Lilium lancifolium. Exogenous treatments with indole-3-acetic acid (IAA) and the auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) were applied to manipulate auxin levels in leaf axils. Results showed that low auxin concentrations, achieved by NPA treatment or silencing of auxin biosynthesis genes LlYUC6 and LlTAR1, significantly enhanced bulbil formation. Histological observations confirmed that bulbil initiation coincided with lower auxin levels and increased expression of sucrose metabolism genes LlSusy1 and LlCWIN2. These genes were found to facilitate sucrose degradation, leading to higher glucose levels that promote bulbil initiation. Additionally, the study identified the transcription factor LlbHLH35, which directly activates LlSusy1 in response to auxin signaling, thus linking auxin content to sucrose metabolism. This research highlights the critical role of the auxin-sucrose module in regulating bulbil initiation, providing a potential strategy to enhance lily propagation through hormonal and metabolic manipulation.
Dr. Jian Wu, a lead researcher in the study, commented, "Our findings reveal a sophisticated interaction between auxin and sucrose metabolism in lily bulbil initiation. By understanding and manipulating these pathways, we can potentially improve vegetative propagation in lilies and other horticultural crops."
The study's insights have major implications for horticulture. Manipulating auxin levels through chemicals or genetics can enhance bulbil formation and improve lily propagation efficiency. This could lead to new techniques that optimize bulb yield and quality, benefiting growers and breeders. Understanding these controls may also enhance propagation methods and yields in other crops.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae054
Funding information
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).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2022. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.