Efficient plant male fertility depends on vegetative nuclear movement mediated by two families of plant outer nuclear membrane proteins

Abstract

Increasing evidence suggests that nuclear migration is important for eukaryotic development. Although nuclear migration is conserved in plants, its importance for plant development has not yet been established. The most extraordinary plant nuclear migration events involve plant fertilization, which is starkly different from that of animals. Instead of evolving self-propelled sperm cells (SCs), plants use pollen tubes to deliver SCs, in which the pollen vegetative nucleus (VN) and the SCs migrate as a unit toward the ovules, a fundamental but barely understood process. Here, we report that WPP domain-interacting proteins (WIPs) and their binding partners the WPP domain-interacting tail-anchored proteins (WITs) are essential for pollen nuclear migration. Loss-offunction mutations in WIT and/or WIP gene families resulted in impaired VN movement, inefficient SC delivery, and defects in pollen tube reception. WIPs are Klarsicht/ANC-1/Syne-1 Homology (KASH) analogs in plants. KASH proteins are key players in animal nuclear migration. Thus, this study not only reveals an important nuclear migration mechanism in plant fertilization but also, suggests that similar nuclear migration machinery is conserved between plants and animals.nuclear envelope | Arabidopsis | male gametophyte | LINC complex N uclear migration is essential for cell differentiation, polarization, and migration, which influence organism development (1-3). Examples range from Caenorhabditis elegans P-cell development to mammalian neural development (1-3). The key players in opisthokont nuclear migration are the inner nuclear membrane Sad1/UNC-84 (SUN) proteins and outer nuclear membrane Klarsicht/ANC-1/Syne-1 Homology (KASH) proteins. SUN and KASH proteins form the linkers of the nucleoskeleton and the cytoskeleton complexes at the nuclear envelope (NE) and transfer cytoplasmic forces to the nucleus (1-3). In plants, nuclear migration is associated with a number of developmental events and environmental responses, including fertilization, root and leaf hair formation, and plant-microbe interactions (4, 5). So far, little is known about the mechanism of plant nuclear migration. Although SUN proteins are conserved in plants (6, 7), absence of animal KASH homologs in plants suggests that plants may have evolved different molecular solutions to achieve nuclear migration. Recently, WPP domaininteracting proteins (WIPs) were identified as KASH proteins in plants (8), and their outer nuclear membrane binding partners WPP domain-interacting tail anchored proteins (WITs) were shown to interact with myosin XI-I (9). The WIT-myosin XI

Update on Myosin Motors: Molecular Mechanisms and Physiological Functions

“…This interpretation also is consistent with Myo11G's very slow ATP hydrolysis cycle (Haraguchi et al, 2016). This unique function of Myo11G, however, seems to be redundant with another myosin in pollen tubes, since wit1 wit2 double mutants show defects in nuclear movement whereas mutants in myo11g (kaku1-4) do not (Zhou and Meier, 2014), demonstrating that other myosin(s) also may be able to bind to WIT1/2.…”

GAP Activity, but Not Subcellular Targeting, Is Required for Arabidopsis RanGAP Cellular and Developmental Functions

“…Thus, protein nucleocytoplasmic trafficking is not visibly impaired in cells in the absence of RanGAP NE association. The fact that both wifi seedlings and soil-grown plants are phenotypically indistinguishable from Col-0 (Zhou and Meier, 2014) indicates that the observed concentration of RanGAP at the NE is neither required for efficient protein nucleocytoplasmic transport nor for the developmental roles revealed by the mutants described above.…”

“…Thus, nuclear import of proteins is not visibly affected in plants with dramatically decreased RanGAP levels. wifi (wip1-1 wip2-1 wip3-1 wit1-1 wit2-1) is a quintuple null mutant in all five WIP and WIT genes, which encode proteins required for concentrating RanGAP1 at the NE (Zhou and Meier, 2014). To compare the effect of reducing overall RanGAP protein abundance with the effect of reducing the amount of NE-associated RanGAP, 35S:RanGAP1-GFP was expressed in wifi.…”

The LINC complex contributes to heterochromatin organisation and transcriptional gene silencing in plants

“…CRWNs are postulated to be components of the plant lamina-like structure and the crwn1 crwn2 double mutant has previously been described to induce small nuclei (Dittmer et al, 2007) and a more condensed chromatin organisation (Grob et al, 2014;van Zanten et al, 2011;Wang et al, 2013). The quintuple wifi mutant (Zhou and Meier, 2014), lacking three KASH proteins WIP1-WIP3 and the two WPP domaininteracting tail-anchored proteins WIT1 and WIT2, was selected to affect the KASH components of the LINC complex as well as some of its interactors located at the outer nuclear membrane. Finally, we combined available sun knockout mutant alleles in the Col-0 background [sun1-1 , sun4-1 and sun5-1 (Graumann et al, 2014)] to obtain double and triple mutants (Fig.…”