Loss of Function of Arabidopsis C-Terminal Domain Phosphatase-Like1 Activates Iron Deficiency Responses at the Transcriptional Level    

Abstract

The expression of genes that control iron (Fe) uptake and distribution (i.e. Fe utilization-related genes) is tightly regulated. Fe deficiency strongly induces Fe utilization-related gene expression; however, little is known about the mechanisms that regulate this response in plants. Transcriptome analysis of an Arabidopsis (Arabidopsis thaliana) mutant defective in RNA polymerase II C-terminal domain-phosphatase-like1 (CPL1) revealed significant up-regulation of Fe utilization-related genes (e.g. IRON-REGULATED TRANSPORTER1), suggesting the importance of RNA metabolism in Fe signaling. An analysis using multiple cpl1 alleles established that cpl1 mutations enhanced specific transcriptional responses to low Fe availability. Changes in protein level were less prominent than those in transcript level, indicating that cpl1-2 mainly affects the Fe deficiency response at the transcriptional level. However, Fe content was significantly increased in the roots and decreased in the shoots of cpl1-2 plants, indicating that the cpl1 mutations do indeed affect Fe homeostasis. Furthermore, root growth of cpl1-2 showed improved tolerance to Fe deficiency and cadmium (Cd) toxicity. cpl1-2 plants accumulated more Cd in the shoots, suggesting that Cd toxicity in the roots of this mutant is averted by the transport of excess Cd to the shoots. Genetic data indicate that cpl1-2 likely activates Fe deficiency responses upstream of both FE-DEFICIENCY-INDUCED TRANSCRIPTION FACTOR-dependent and -independent signaling pathways. Interestingly, various osmotic stress/abscisic acid (ABA)-inducible genes were up-regulated in cpl1-2, and the expression of some ABA-inducible genes was controlled by Fe availability. We propose that the cpl1 mutations enhance Fe deficiency signaling and promote cross talk with a branch of the osmotic stress/ABA signaling pathway.

The Protein Phosphatase RCF2 and Its Interacting Partner NAC019 Are Critical for Heat Stress–Responsive Gene Regulation and Thermotolerance in Arabidopsis

“…Aksoy et al (2013) also reported in a microarray study that 132 genes are downregulated in the cpl1-2/fry2-1 mutant plants under unstressed conditions, although further investigation was needed to elucidate how CPL1/FRY2 controls the expression of these genes in a positive manner. The observation that the expression of RCF2/CPL1/FRY2 is upregulated by heat stress motivated us to investigate the role of RCF2 in heat stress responses (Supplemental Figure 5B).…”

“…The precise mechanisms by which RCF2/CPL1/FRY2 preferentially affects cold, ABA, NaCl, and wounding responses remain unknown. From microarray analysis, Aksoy et al (2013) showed that 114 genes were upregulated in the cpl1-2/fry2-1 mutant plants under unstressed conditions and that CPL1 appears to repress the expression of genes encoding the signaling components downstream of iron deficiency by an unknown mechanism.…”

Molecular mechanisms governing Arabidopsis iron uptake

“…CPL1 has been shown to interact with REGULATOR OF CBF GENE EXPRESSION 3 (RCF3), the absence of which also leads to an accumulation of Fe-responsive mRNAs [54] ( Figure 1B). However, reporter gene fusion experiments have shown that CPL1 is not expressed in the root epidermis where FRO2 and IRT1 are active [53]. Although the exact role of CPL1 as a RNA polymerase II regulatory subunit is not clear, the presence of the double-stranded RNA-binding domain suggests that CPL1 may be involved in cotranscriptional mRNA processing.…”

“…Another subunit of the RNA polymerase II complex, RNA POL II C-TERMINAL DOMAIN-LIKE PHOSPHATASE 1 (CPL1), has been shown to act upstream of FIT, negatively affecting the mRNA availability of FIT, subgroup Ib bHLH genes, and, subsequently, FRO2 and IRT1 ( Figure 1B). For several of these genes, the effect is visible only in the first days of Fe deficiency [53]. CPL1 has been shown to interact with REGULATOR OF CBF GENE EXPRESSION 3 (RCF3), the absence of which also leads to an accumulation of Fe-responsive mRNAs [54] ( Figure 1B).…”

Ascorbate Alleviates Fe Deficiency-Induced Stress in Cotton (Gossypium hirsutum) by Modulating ABA Levels

“…For the exogenous application of ABA could induce the accumulation of ferritin mRNA (Lobreaux et al, 1993). A set of ABA and osmotic stress response genes are co-regulated by Fe signaling or by the gene CPL1-2 ( RNA polymerase II C-terminal domain-phosphatase-like1 ) which act upstream of FIT, negatively affecting the mRNA availability of FIT1 , FRO2 and IRT1 in Arabidopsis (Aksoy et al, 2013). However, the molecular mechanism of ABA involved in Fe deficiency in plant is still unknown, even though it has been shown that ABI5 is involved in the ABA-mediated alleviation of chlorosis under Fe deficiency in Arabidopsis (Lei et al, 2014).…”