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Abstract Pollen tube attraction is a key event of sexual reproduction in flowering plants. In the ovule, two synergid cells neighboring the egg cell control pollen tube arrival via the active secretion of attractant peptides such as AtLURE1 and XIUQIU from the filiform apparatus (FA) facing toward the micropyle. Distinctive cell polarity together with longitudinal F-actin and microtubules are hallmarks of the synergid cell in various species, though the functions of these cellular structures are unclear. In this study, we used genetic and pharmacological approaches to indicate the roles of cytoskeletal components in FA formation and pollen tube guidance in Arabidopsis thaliana. Genetic inhibition of microtubule formation reduced invaginations of the plasma membrane but did not abolish micropylar AtLURE1.2 accumulation. By contrast, the expression of a dominant-negative form of ACTIN8 induced disorganization of the FA and loss of polar AtLURE1.2 distribution toward the FA. Interestingly, after pollen tube reception, F-actin became unclear for a few hours in the persistent synergid cell, which may be involved in pausing and resuming pollen tube attraction during early polytubey block. Our data suggest that F-actin plays a central role in maintaining cell polarity and in mediating male–female communication in the synergid cell.
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Regulation of MILDEW RESISTANCE LOCUS-O trafficking by calmodulin-binding domains
Abstract Flowering plant sexual reproduction relies on the communication between the pollen tube and synergid cells to induce pollen tube bursting. During this process, the MILDEW RESISTANCE LOCUS-O (MLO) protein NORTIA (NTA) is polarly trafficked from the Golgi, where it is inactive, to the filiform apparatus, where it is functional in synergids. MLOs were recently described as calcium channels and have been proposed to be negatively regulated through calmodulin (CaM) binding at a conserved C-terminal calmodulin-binding domain (CaMBD). To determine whether CaM binding is necessary for MLO function during pollen tube reception, C-terminal truncations and CaMBD point mutations were made in NTA. Point mutations were also generated in a constitutively filiform apparatus-localized chimeric NTA containing the MLO1 C-terminus. In this study, we demonstrate that mutating the MLO1 and NTA CaMBD reduces the ability for MLOs to function during pollen tube reception. This is in part due to altered subcellular localization of the CaMBD mutants in synergids. We showed that the CaMBD is not necessary for Golgi localization of MLOs, but is necessary for efficient trafficking and total protein accumulation at the filiform apparatus. Our results suggest an additional role for CaM binding as a regulator of MLO trafficking in addition to its previously proposed role as a negative regulator of MLO Ca2+ channel activity.
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- Award ID(s):
- 2224038
- PAR ID:
- 10629599
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Journal of Experimental Botany
- Volume:
- 76
- Issue:
- 12
- ISSN:
- 0022-0957
- Format(s):
- Medium: X Size: p. 3332-3344
- Size(s):
- p. 3332-3344
- Sponsoring Org:
- National Science Foundation
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