Vegetative nuclear positioning is required for calcium and ROS signaling in Arabidopsis pollen tubes

AbstractEfficient transport and delivery of sperm cells (SCs) is vital for angiosperm plant fertility. In Arabidopsis thaliana, SCs are transported through the growing pollen tube by a connection with the vegetative nucleus (VN). During pollen tube growth, the VN leads the way and maintains a fixed distance from the pollen tube tip, while the SCs lag behind the VN. Upon reception at the ovule, the pollen tube bursts and the SCs are released for fertilization. In pollen tubes of Arabidopsis mutants wit12 and wifi, deficient in the outer nuclear membrane component of a plant LINC complex, the SCs precede the VN and the VN falls behind. Subsequently, pollen tubes frequently fail to burst upon reception. In this study, we sought to determine if the pollen tube reception defect observed in wit12 and wifi is due to decreased sensitivity to reactive oxygen species (ROS). Here we show that wit12 and wifi are hyposensitive to exogenous H2O2, and that this hyposensitivity is correlated with decreased proximity of the VN to the pollen tube tip. Additionally, we report the first instance of nuclear Ca2+ spikes in growing pollen tubes, which are disrupted in the wit12 mutant. In the wit12 mutant, nuclear Ca2+ spikes are reduced in response to exogenous ROS, but these spikes are not correlated with pollen tube burst. This study finds that VN proximity to the pollen tube tip is required for both response to exogenous ROS, as well as internal nuclear Ca2+ fluctuations.SummaryMutants deficient in outer nuclear membrane proteins display defects in reactive oxygen species-induced pollen tube burst and nuclear Ca2+ signatures that correlate with the position of the vegetative nucleus.

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Arabidopsis ABCG28 is required for the apical accumulation of reactive oxygen species in growing pollen tubes

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1902010116 ◽

2019 ◽

Vol 116 (25) ◽

pp. 12540-12549 ◽

Cited By ~ 6

Author(s):

Thanh Ha Thi Do ◽

Hyunju Choi ◽

Michael Palmgren ◽

Enrico Martinoia ◽

Jae-Ung Hwang ◽

...

Keyword(s):

Reactive Oxygen Species ◽

Pollen Tube ◽

Pollen Tube Growth ◽

Tip Growth ◽

Ectopic Expression ◽

Reactive Oxygen ◽

Pollen Tubes ◽

Tube Growth ◽

Oxygen Species ◽

Ros Accumulation

Tip-focused accumulation of reactive oxygen species (ROS) is tightly associated with pollen tube growth and is thus critical for fertilization. However, it is unclear how tip-growing cells establish such specific ROS localization. Polyamines have been proposed to function in tip growth as precursors of the ROS, hydrogen peroxide. The ABC transporter AtABCG28 may regulate ROS status, as it contains multiple cysteine residues, a characteristic of proteins involved in ROS homeostasis. In this study, we found that AtABCG28 was specifically expressed in the mature pollen grains and pollen tubes. AtABCG28 was localized to secretory vesicles inside the pollen tube that moved toward and fused with the plasma membrane of the pollen tube tip. Knocking out AtABCG28 resulted in defective pollen tube growth, failure to localize polyamine and ROS to the growing pollen tube tip, and complete male sterility, whereas ectopic expression of this gene in root hair could recover ROS accumulation at the tip and improved the growth under high-pH conditions, which normally prevent ROS accumulation and tip growth. Together, these data suggest that AtABCG28 is critical for localizing polyamine and ROS at the growing tip. In addition, this function of AtABCG28 is likely to protect the pollen tube from the cytotoxicity of polyamine and contribute to the delivery of polyamine to the growing tip for incorporation into the expanding cell wall.

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PbrRALF2-elicited reactive oxygen species signaling is mediated by the PbrCrRLK1L13-PbrMPK18 module in pear pollen tubes

Horticulture Research ◽

10.1038/s41438-021-00684-y ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Xiaobing Kou ◽

Jiangmei Sun ◽

Peng Wang ◽

Danqi Wang ◽

Peng Cao ◽

...

Keyword(s):

Reactive Oxygen Species ◽

Pollen Tube ◽

Pollen Tube Growth ◽

Reactive Oxygen ◽

Pollen Tubes ◽

Tube Growth ◽

General Mechanism ◽

Dependent Manner ◽

Ros Production ◽

Oxygen Species

AbstractRapid alkalinization factors (RALFs) are cysteine-rich peptides that play important roles in a variety of biological processes, such as cell elongation and immune signaling. Recent studies in Arabidopsis have shown that RALFs regulate pollen tube growth via plasma membrane receptor-like kinases (RLKs). However, the downstream signal transduction mechanisms of RLKs in pollen tubes are unknown. Here, we identified PbrRALF2, a pear (Pyrus bretschneideri) pollen RALF peptide that inhibits pollen tube growth. We found that PbrRALF2 interacts with a malectin-like domain-containing RLK, PbrCrRLK1L13. The relative affinity between PbrRALF2 and PbrCrRLK1L13 was at the submicromolar level, which is consistent with the values of ligand–receptor kinase pairs and the physiological concentration for PbrRALF2-mediated inhibition of pollen tube growth. After binding to its extracellular domain, PbrRALF2 activated the phosphorylation of PbrCrRLK1L13 in a dose-dependent manner. We further showed that the MAP kinase PbrMPK18 is a downstream target of PbrCrRLK1L13 that mediates PbrRALF2-elicited reactive oxygen species (ROS) production. The excessive accumulation of ROS inhibits pollen tube growth. We show that MPK acts as a mediator for CrRLK1L to stimulate ROS production, which might represent a general mechanism by which RALF and CrRLK1L function in signaling pathways.

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