Cytoskeleton, Transglutaminase and Gametophytic Self-Incompatibility in the Malinae (Rosaceae)

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.

Compatible and Incompatible Pollen-Styles Interaction in Pyrus communis L. Show Different Transglutaminase Features, Polyamine Pattern and Metabolomics Profiles

“…In the last decades, both genetic and molecular factors involved in SI have been studied in Malinae, as GSI affects both quantitative and qualitative aspects of productivity in agricultural species of great economic interest (Del Duca et al, 2019). In the GSI of Malinae, the stylar S locus plays an important role, since it encodes for glycoproteins with ribonuclease (S-RNase) activities that enter inside the pollen tube.…”

“…Several evidences highlight the involvement of transglutaminase (TGase) in the process of pollen rejection, not only in Malinae (Gentile et al, 2012; Aloisi et al, 2016a; Del Duca et al, 2019). TGases are ubiquitous enzymes that catalyze the post-translational modification of proteins, through the incorporation of primary amines or by protein cross-linking, resulting often in high molecular mass products (Griffin et al, 2002).…”

Temperature-Dependent Compatible and Incompatible Pollen-Style Interactions in Citrus clementina Hort. ex Tan. Show Different Transglutaminase Features and Polyamine Pattern

“…In order to avoid self-fertilization, plants have adopted different strategies, among which, the asynchronous development of male and female organs, their specific localization within the flower or in the tree crown, and genetics-based strategies ( Del Duca et al., 2019 ), the latter defined as “self-incompatibility” (SI). SI consists in the rejection of pollen from genetically related individuals (“self” pollen) thus preventing inbreeding and finally promoting outcrossing.…”

The Artificial Promoter rMdAG2I Confers Flower-specific Activity in Malus

“…Flowering crabapples belonging to this genus are widely used in landscape gardening, due to their varied and attractive flower color, size and fragrance [2]. Malus plants are always self-sterile, requiring cross-pollination by insects, such as bees, which is important for fruit production in domesticated apples [3,4,5,6,7]. Flowers are key reproductive organs, because they play important roles in attracting pollinating insects.…”