Abstract
The lotus produces flower buds at each node, yet most of them are aborted because of unfavorable environmental changes and the mechanism remains unclear. In this work, we proposed a potential novel pathway for ABA-mediated flower timing control in the lotus, which was explored by combining molecular, genetic, transcriptomic, biochemical, and pharmacologic approaches. We found that the aborting flower buds experienced extensive programmed cell death (PCD). The hormonal changes between the normal and aborting flower buds were dominated by abscisic acid (ABA). Seedlings treated with increasing concentrations of ABA exhibited a differential alleviating effect on flower bud abortion, with a maximal response at 80 μM. Transcriptome analysis further confirmed the changes of ABA content and the occurrence of PCD, and indicated the importance of PCD-related SNF1-related protein kinase 1 (NnSnRK1). The NnSnRK1-silenced lotus seedlings showed stronger flowering ability, with their flower:leaf ratio increased by 40%. When seedlings were treated with ABA, the expression level and protein kinase activity of NnSnRK1 significantly decreased. The phenotype of NnSnRK1-silenced seedlings could also be enhanced by ABA treatment and reversed by tungstate treatment. These results suggested that the decline of ABA content in lotus flower buds released its repression of NnSnRK1, which then initiated flower bud abortion.
Highlights
Proper flowering timing determines the reproductive success of plants [1]
Adverse environmental changes that limit photosynthesis and alter carbohydrate levels often lead to aborted flower buds, i.e., leaf shading by other leaves and rainy weather (Figure 1B), which led to a flower bud abortion rate over 80% in the variety used in this study
Flower bud abortion exists in other plants, such as the tree peony [12] and rose [13]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Plants demonstrate sophisticated mechanisms to integrate diverse environmental cues and endogenous signals to ensure survival and reproductive success [1]. Accumulating evidence suggest the functional link between flowering time, sugar levels, and sucrose nonfermenting-1 (SNF1)-related protein kinases 1 (SnRK1) activity. INDETERMINATE DOMAIN (IDD8) transcription factor is identified as a downstream target of SnRK1, which regulates flowering time by modulating sugar metabolism, sensing, and transport [10]. Adverse environmental conditions reduce reproductive success, slow seed and fruit development, and even threaten survival. This different strategy could help the lotus to terminate flowering with low reproductive success and minimize energy waste, yet the mechanism remains unclear. We conducted an integrated analysis of morphological and cytological observations, endogenous phytohormone assay, high throughput sequencing, and transgenic validations to uncover the underlying regulatory mechanism
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