The intriguing plant nuclear lamina

Abstract

The nuclear lamina is a complex protein mesh attached to the inner nuclear membrane (INM), which is also associated with nuclear pore complexes. It provides mechanical support to the nucleus and nuclear envelope, and as well as facilitating the connection of the nucleoskeleton to the cytoskeleton, it is also involved in chromatin organization, gene regulation, and signaling. In metazoans, the nuclear lamina consists of a polymeric layer of lamins and other interacting proteins responsible for its association with the INM and chromatin. In plants, field emission scanning electron microscopy of nuclei, and thin section transmission electron microscopy of isolated nucleoskeletons, reveals the lamina to have a similar structure to that of metazoans. Moreover, although plants lack lamin genes and the genes encoding most lamin-binding proteins, the main functions of the lamina are fulfilled in plants. Hence, it would appear that the plant lamina is not based on lamins and that other proteins substitute for lamins in plant cells. The nuclear matrix constituent proteins are the best characterized structural proteins in the plant lamina. Although these proteins do not display strong sequence similarity to lamins, their predicted secondary structure and sub-nuclear distribution, as well as their influence on nuclear size and shape, and on heterochromatin organization, suggest they could be functional lamin analogs. In this review we shall summarize what is currently known about the organization and composition of the plant nuclear lamina and its interacting complexes, and we will discuss the activity of this structure in the plant cell and its nucleus.

Plant nuclear shape is independently determined by the SUN-WIP-WIT2-myosin XI-i complex and CRWN1

“…15 NMCP/CRWN proteins are coiled-coil proteins isolated from plant nuclear fractions and are proposed to share structural similarity to lamins. 15,16,19 The Arabidopsis genome encodes 4 CRWN genes, but only CRWN1 and CRWN4 are localized to the nuclear periphery. 19,20 CRWN1 and CRWN4 single mutants have small, round nuclei but show no developmental phenotypes.…”

“…14 However, no lamin homologs have been found in plant proteomes. 15 Instead, Nuclear Matrix Constituent Proteins (NMCP) [16][17][18] and their Arabidopsis homologs, CROWDED NUCLEI (CRWN, also known as LITTLE NUCLEI) proteins, were identified as putative analogs of mammalian lamins in plants. 15 NMCP/CRWN proteins are coiled-coil proteins isolated from plant nuclear fractions and are proposed to share structural similarity to lamins.…”

“…15 Instead, Nuclear Matrix Constituent Proteins (NMCP) [16][17][18] and their Arabidopsis homologs, CROWDED NUCLEI (CRWN, also known as LITTLE NUCLEI) proteins, were identified as putative analogs of mammalian lamins in plants. 15 NMCP/CRWN proteins are coiled-coil proteins isolated from plant nuclear fractions and are proposed to share structural similarity to lamins. 15,16,19 The Arabidopsis genome encodes 4 CRWN genes, but only CRWN1 and CRWN4 are localized to the nuclear periphery.…”

Nonrandom domain organization of the Arabidopsis genome at the nuclear periphery

“…This is largely because plant genomes do not encode proteins with sequences similar to those of nuclear lamins in animals, although in several plant species, a meshwork similar to the nuclear lamina beneath the nuclear envelope has been observed (Ciska and Moreno Díaz de la Espina 2014). Nevertheless, over the past few years, a group of plant-specific nuclear matrix constituent proteins (NMCPs), such as CROWDED NUCLEI (CRWN) in Arabidopsis, have emerged as "plant lamina" components (Ciska and Moreno Díaz de la Espina 2014; Zhou et al 2015).…”

A nuclear contortionist: the mitotic migration ofMagnaporthe oryzaenuclei during plant infection

“…Fungal nuclei are known to be flexible, largely attributed to the fact that fungi lack true lamin proteins (Steinberg et al 2012; Ciska and Moreno Díaz De La 2014). The nuclei of fungi such as U. maydis (Straube et al 2005), Neurospora crassa (Roca et al 2010), and Candida albicans (Finley and Berman 2005) all display some degree of elongation during migration.…”