Spatial and Temporal Distribution of Arabinogalactan Proteins during Larix decidua Mill. Male Gametophyte and Ovule Interaction.

Katarzyna Rafińska,Elżbieta Bednarska-Kozakiewicz,Michał Świdziński,Katarzyna Niedojadło,Janusz Niedojadło

doi:10.3390/ijms22094298

Katarzyna Rafińska, Elżbieta Bednarska-Kozakiewicz + Show 3 more

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https://doi.org/10.3390/ijms22094298

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Abstract

The role of ArabinoGalactan Proteins (AGPs) in the sexual reproduction of gymnosperms is not as well documented as that of angiosperms. In earlier studies, we demonstrated that AGPs play important roles during ovule differentiation in Larix decidua Mill. The presented results encouraged us to carry out further studies focused on the functions of these unique glycoproteins during pollen/pollen tube and ovule interactions in Larix. We identified and analyzed the localization of AGPs epitopes by JIM4, JIM8, JIM13 and LM2 antibodies (Abs) in male gametophytes and ovule tissue during pollination, the progamic phase, and after fertilization and in vitro growing pollen tubes. Our results indicated that (1) AGPs recognized by JIM4 Abs play an essential role in the interaction of male gametophytes and ovules because their appearance in ovule cells is induced by physical contact between reproductive partners; (2) after pollination, AGPs are secreted from the pollen cytoplasm into the pollen wall and contact the extracellular matrix of stigmatic tip cells followed by micropylar canal cells; (3) AGPs synthesized in nucellus cells before pollen grain germination are secreted during pollen tube growth into the extracellular matrix, where they can directly interact with male gametophytes; (4) in vitro cultured pollen tube AGPs labeled with LM2 Abs participate in the germination of pollen grain, while AGPs recognized by JIM8 Abs are essential for pollen tube tip growth.

Highlights

IntroductionThe interaction results in a change in the activity of the wall enzymes of both reproductive partners, leading to alterations in the composition of the extracellular matrix (ecm), including the level of Ca2+ ions relevant for germination, pollen tube growth and double fertilization [5,6,7]
In the mature, hydrated pollen grain, all examined ArabinoGalactan Proteins (AGPs) were present in the cytoplasm of pollen cells (Figure 2A–D), excluding prothallial cells, where the JIM4 Abs signal was not observed (Figure 2A)
Our studies reveal that in L. decidua, AGPs are involved in the interaction between the male gametophyte and the ovule: 1

Summary

Introduction

The interaction results in a change in the activity of the wall enzymes of both reproductive partners, leading to alterations in the composition of the extracellular matrix (ecm), including the level of Ca2+ ions relevant for germination, pollen tube growth and double fertilization [5,6,7]. Given their unique structural properties, such as the diversity of the core protein, GPI (glycosylphosphatidylinositol) anchor and heterogeneity of the glycan chains, the large family of AGPs represents crucial candidates in these processes [8,9,10].

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