The Immunophilin-Interacting Protein AtFIP37 from Arabidopsis Is Essential for Plant Development and Is Involved in Trichome Endoreduplication

Abstract

The FKBP12 (FK506-binding protein 12 kD) immunophilin interacts with several protein partners in mammals and is a physiological regulator of the cell cycle. In Arabidopsis, only one specific partner of AtFKBP12, namely AtFIP37 (FKBP12 interacting protein 37 kD), has been identified but its function in plant development is not known. We present here the functional analysis of AtFIP37 in Arabidopsis. Knockout mutants of AtFIP37 show an embryo-lethal phenotype that is caused by a strong delay in endosperm development and embryo arrest. AtFIP37 promoter::b-glucuronidase reporter gene constructs show that the gene is expressed during embryogenesis and throughout plant development, in undifferentiating cells such as meristem or embryonic cells as well as highly differentiating cells such as trichomes. A translational fusion with the enhanced yellow fluorescent protein indicates that AtFIP37 is a nuclear protein localized in multiple subnuclear foci that show a speckled distribution pattern. Overexpression of AtFIP37 in transgenic lines induces the formation of large trichome cells with up to six branches. These large trichomes have a DNA content up to 256C, implying that these cells have undergone extra rounds of endoreduplication. Altogether, these data show that AtFIP37 is critical for life in Arabidopsis and implies a role for AtFIP37 in the regulation of the cell cycle as shown for FKBP12 and TOR (target of rapamycin) in mammals.Immunophilins are a family of enzymes with a peptidyl-prolyl cis-trans isomerase activity (PPiase) involved in the folding of target proteins (Kay, 1996;Schiene-Fischer and Yu, 2001;Hur and Bruice, 2002;Shaw, 2002). Their function has been primarily studied in human immune response as they are receptors for immunosuppressive drugs. Among immunophilins, FK506-binding proteins (FKBPs) are intracellular receptors for the two related drugs, FK506 and rapamycin. FKBPs are found in many organisms, including prokaryotes, animals, and plants (Harrar et al., 2001;Breiman and Camus, 2002).While FKBPs differ in size, FKBP12 (12 kD) represents the minimal peptide sequence harboring the two main properties of FKBPs, namely the PPiase activity and drug binding. FKBP12 is a ubiquitous and abundant protein localized in the cytosol of mammalian cells (Maki et al., 1990). In mammals, FKBP12 is essential since a knockout mouse dies during embryonic development (Shou et al., 1998), while in yeast (Saccharomyces cerevisiae) loss of FKBP12 function does not affect cell viability (Dolinski et al., 1997). In the absence of drugs, FKBP12 is associated with receptors such as the type II-TGFb (transforming growth factor b) receptor or calcium channels such as the ryanodine receptor or the inositol-(1,4,5)-triphosphate receptor (Ins(1,4,5)P 3 R). When bound to FK506, FKBP12 dissociates from the receptors resulting in a misregulation of receptor activities. For instance, the activity of the TGFb receptor is leaky in the absence of ligand after the release of FKBP12 by FK506 leading to the inactivation by dephosphoryla...

Chlamydomonas Immunophilins and Parvulins: Survey and Critical Assessment of Gene Models

“…It is the one represented by the largest number of ESTs and also the only single-domain FKBP unambiguously targeted to the cytosol. It is similar to the well-characterized cytosolic FKBP12 that interacts with the mTOR protein kinase required for cell cycle progression (7) and in Arabidopsis with AtFIP37, a phosphatidyl-inositol kinase essential for development (34). In the phylogenetic tree ( Fig.…”

Identification of factors required for m6A mRNA methylation in Arabidopsis reveals a role for the conserved E3 ubiquitin ligase HAKAI

“…Null mutations in MTA are embryonic lethal (Zhong et al ., 2008), as are null alleles of Arabidopsis MTB , FIP37 and VIRILIZER (Tzafrir et al ., 2004; Vespa et al ., 2004). However, we identified a viable hypomorphic allele of FIP37 , caused by a T‐DNA insertion within its 7 th intron ( fip37‐4 , identical to that described in Shen et al .…”

“…m 6 A has recently been shown to have a crucial role during murine stem cell development, where it prompts stem cell differentiation from their naïve stage (Geula et al ., 2015). Arabidopsis full knockouts of MTA, MTB, FIP37 and VIR also do not progress past the embryonic globular stage (Tzafrir et al ., 2003; Vespa et al ., 2004; Zhong et al ., 2008). We have circumvented this embryo lethality by establishing a collection of hypomorphic, mutants or RNAi lines for each of the proteins associated with the m 6 A writer complex in order to study the effects of reduced m 6 A in postembryonic development.…”

RNA N6-methyladenosine methylation in post-transcriptional gene expression regulation

“…Intriguingly, MTA tends to be expressed in higher levels in dividing tissues, such as developing seeds, shoot meristems, and emerging lateral roots (Craigon et al 2004;Zhong et al 2008). Disruption of either MTA or FIP37 in Arabidopsis leads to developmental arrest of embryos at the globular stage (Vespa et al 2004;Zhong et al 2008), coupled to a loss of m 6 A from the mRNA in arrested seeds (Vespa et al 2004;Zhong et al 2008). Later in development, perturbation of MTA causes multiple growth defects, including reduced apical dominance, organ abnormality, and increased trichome branching (Bodi et al 2012).…”