Altered metal distribution in thesr45-1Arabidopsis mutant causes developmental defects

Abstract

The plant SR (serine/arginine-rich) splicing factor SR45 plays important roles in several biological processes, such as splicing, DNA methylation, innate immunity, glucose regulation and ABA signaling. A homozygous Arabidopsis sr45-1 null mutant is viable, but exhibits diverse phenotypic alterations, including delayed root development, late flowering, shorter siliques with fewer seeds, narrower leaves and petals, and unusual numbers of floral organs. Here, we report that the sr45-1 mutant presents an unexpected constitutive iron deficiency phenotype characterized by altered metal distribution in the plant. RNA-Sequencing highlighted severe perturbations in metal homeostasis, phenylpropanoid pathway, oxidative stress responses, and reproductive development. Ionomic quantification and histochemical staining revealed strong iron accumulation in the sr45-1 root tissues accompanied by an iron starvation in aerial parts. We showed that some sr45-1 developmental abnormalities can be complemented by exogenous iron supply. Our findings provide new insight into the molecular mechanisms governing the phenotypes of the sr45-1 mutant.

FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT) accumulates in homo- and heterodimeric complexes in dynamic and inducible nuclear condensates associated with speckle components

“…The characterization of FIT NBs as speckles is interesting because regulation of splicing and epigenetic regulation is associated with iron deficiency gene expression. Genes were spliced incorrectly in a sr45-1 null mutant Arabidopsis line, and gene expression of FIT and FIT target genes was increased in sr45-1 seedlings, showing that an interplay between SR45 and the iron uptake machinery exists (Fanara et al, 2022). Alternative splicing was detected for FIT targets and the BHLH subgroup Ib genes in iron-deficient versus iron-sufficient conditions (Li et al, 2013).…”

“…This included the speckle components ARGININE/SERINE-RICH45-mRFP (SR45) and the serine/arginine-rich matrix protein SRm102-mRFP (Figure 5). SR45 is involved in splicing and alternative splicing and is part of the spliceosome in speckles (Ali et al, 2003), and was recently found to be involved in splicing of iron homeostasis genes (Fanara et al, 2022). SRm102 is a speckle component (Kim et al, 2016).…”

“…These processes fit well to the described FIT NB attributes. The characterization of FIT NBs as speckles is interesting because regulation of splicing and epigenetic regulation is associated with both, iron deficiency gene expression and SR45 (Fanara et al, 2022;Mikulski et al, 2022). UAP56H2, P15H1, and PININ (type III) are connected to SR45 and SRm102 (type II) in mammalian cells as all being part of the exon junction complex and interacting with each other (Lin et al, 2004;Pendle et al, 2005).…”