The peptide, named NON-DEFENSIN PEPTIDE ATTRACTANT 1 (NPA1), represents the first non-defensin-type attractant identified in dicots and expands the known diversity of fertilization cues in flowering plants. Unlike the commonly known cysteine-rich peptides (CRPs) such as LUREs, NPA1 operates independently of the typical defensin-like structure.
Successful fertilization in flowering plants depends on precise communication between male and female gametophytes. After pollen lands on a stigma, a tube grows towards the ovule, guided by attractant peptides secreted by the female synergid cells. In dicots, all previously identified attractants—such as LUREs and XIUQIUs—belong to the defensin-like CRP family. These peptides are structurally stabilized by multiple cysteines and are tightly regulated by the transcription factor MYB98. However, despite the identification of over ten CRP-type attractants in Arabidopsis, partial defects in pollen tube targeting suggested the existence of additional, unidentified cues. Due to these gaps, further research was needed to uncover novel attractants and elucidate their roles in reproductive success.
A study (DOI: 10.48130/seedbio-0024-0001) published in Seed Biology on 21 February 2024 by Hong-Ju Li’s team, University of Chinese Academy of Sciences, not only challenges longstanding assumptions about pollen tube guidance in dicots but also highlights the evolutionary plasticity of reproductive signaling systems in angiosperms.
To identify novel non-defensin peptides involved in pollen tube attraction in Arabidopsis thaliana, researchers analyzed transcriptomic datasets to screen for genes downregulated in myb98 mutants, selectively expressed in synergid cells, and lacking CRP motifs. This approach revealed six candidate genes, among which AT4G02655—named NPA1—was highly expressed in ovules and contained a secretion signal. Its homolog, AT1G18486 (NPA2), was similarly identified. RT-PCR and GFP fusion constructs confirmed that both genes are synergid-specific and transcriptionally regulated by MYB98. Structural modeling showed that NPA1 and NPA2 differ from typical CRPs by forming five α-helices with two disulfide bonds, lacking the defensin-like motifs. Functional assays using purified recombinant peptides demonstrated that NPA1—but not NPA2—can attract pollen tubes in semi-in vitro systems, although with lower potency than the known attractant LURE1.2. Mutation of four conserved cysteines abolished NPA1’s attraction and membrane-binding abilities, confirming their functional importance. NPA1 was also shown to preferentially attract conspecific and closely related species’ pollen tubes, indicating its role in species-preferential fertilization. Furthermore, expression of NPA1 in myb98 mutants significantly rescued pollen tube guidance and increased seed set, but did not fully restore fertilization success, highlighting its specific role in guidance rather than post-fertilization events. Collectively, these results establish NPA1 as a novel non-defensin peptide attractant functioning in the MYB98 pathway, expanding the known repertoire of reproductive signaling peptides in plants.
The identification of NPA1 broadens the landscape of peptide signaling in plant fertilization and offers new molecular tools for crop breeding. Since hybridization and interspecific crosses are often limited by species-specific fertilization signals, understanding peptides like NPA1 can help overcome reproductive barriers. Moreover, synthetic manipulation of such attractants could improve fertilization rates in agricultural systems or help engineer novel traits in seed production. Ultimately, this research suggests that plants, like animals, have evolved a diverse set of signaling peptides for reproductive coordination.
###
References
DOI
10.48130/seedbio-0024-0001
Original Source URL
https://doi.org/10.48130/seedbio-0024-0001
Funding information
The work was supported by the National Key Research and Development Program of China (2022YFF1003500), National Natural Science Foundation (32170343), and CAS Project for Young Scientists in Basic Research (No.YSBR-078).
About Seed Biology
Seed Biology (e-ISSN 2834-5495) is published by Maximum Academic Press in partnership with Yazhou Bay Seed Laboratory. Seed Biology is an open access, online-only journal focusing on research related to all aspects of the biology of seeds, including but not limited to: evolution of seeds; developmental processes including sporogenesis and gametogenesis, pollination and fertilization; apomixis and artificial seed technologies; regulation and manipulation of seed yield; nutrition and health-related quality of the endosperm, cotyledons, and the seed coat; seed dormancy and germination; seed interactions with the biotic and abiotic environment; and roles of seeds in fruit development. Seed biology publishes a wide range of research approaches, such as omics, genetics, biotechnology, genome editing, cellular and molecular biology, physiology, and environmental biology. Seed Biology publishes high-quality original research, reviews, perspectives, and opinions in open access mode, promoting fast submission, review, and dissemination freely to the global research community.