Abstract
Self-incompatibility (SI) is a complex process, one out of several mechanisms that prevent plants from self-fertilizing to maintain and increase the genetic variability. This process leads to the rejection of the male gametophyte and requires the co-participation of numerous molecules. Plants have evolved two distinct SI systems, the sporophytic (SSI) and the gametophytic (GSI) systems. The two SI systems are markedly characterized by different genes and proteins and each single system can also be divided into distinct subgroups; whatever the mechanism, the purpose is the same, i.e., to prevent self-fertilization. In Malinae, a subtribe in the Rosaceae family, i.e., Pyrus communis and Malus domestica, the GSI requires the production of female determinants, known as S-RNases, which penetrate the pollen tube to interact with the male determinants. Beyond this, the penetration of S-RNase into the pollen tube triggers a series of responses involving membrane proteins, such as phospholipases, intracellular variations of cytoplasmic Ca2+, production of reactive oxygen species (ROS) and altered enzymatic activities, such as that of transglutaminase (TGase). TGases are widespread enzymes that catalyze the post-translational conjugation of polyamines (PAs) to different protein targets and/or the cross-linking of substrate proteins leading to the formation of cross-linked products with high molecular mass. When actin and tubulin are the substrates, this destabilizes the cytoskeleton and inhibits the pollen-tube’s growth process. In this review, we will summarize the current knowledge of the relationship between S-RNase penetration, TGase activity and cytoskeleton function during GSI in the Malinae.
Highlights
The Molecular Basis of showing ribonuclease (S-RNase)-Based Gametophytic Self-Incompatibility in the MalinaeIn plants, from the less to the more complex species, the reproductive process can take various forms, from the vegetative one, which ensures the spread of individuals without genetic changes, up to sexual reproduction
In Malinae, a subtribe in the Rosaceae family, i.e., Pyrus communis and Malus domestica, the gametophytic SI (GSI) requires the production of female determinants, known as S-RNases, which penetrate the pollen tube to interact with the male determinants
The above examples come from a different SI system and should be taken with caution when trying to adapt them to the Malinae system; they suggest that the cytoskeleton of pollen tubes may be part of the complex mechanism that regulates the programmed-cell death (PCD) progress during SI response
Summary
The Molecular Basis of S-RNase-Based Gametophytic Self-Incompatibility in the Malinae. Other processes, including changes in cytoplasmic Ca2+ concentration and actin filaments (AFs) alteration, are likely to be involved [12] This Ca2+-signaling cascade leads downstream to pollen tube tip growth arrest, depolymerization of AFs and programmed-cell death (PCD) [13]. Both pollen-style interaction and SI response occur with different mechanisms in different plant families; since. The above examples come from a different SI system and should be taken with caution when trying to adapt them to the Malinae system; they suggest that the cytoskeleton of pollen tubes (both AFs and MTs) may be part of the complex mechanism that regulates the PCD progress during SI response
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