Abstract
As an essential nutrient, copper (Cu) scarcity causes a decrease in agricultural production. Cu deficiency responses include the induction of several microRNAs, known as Cu-miRNAs, which are responsible for degrading mRNAs from abundant and dispensable cuproproteins to economize copper when scarce. Cu-miRNAs, such as miR398 and miR408 are conserved, as well as the signal transduction pathway to induce them under Cu deficiency. The Arabidopsis thaliana SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) family member SPL7 binds to the cis-regulatory motifs present in the promoter regions of genes expressed under Cu deficiency, including Cu-miRNAs. The expression of several other SPL transcription factor family members is regulated by miR156. This regulatory miR156-SPL module plays a crucial role in developmental phase transitions while integrating internal and external cues. Here, we show that Cu deficiency also affects miR156 expression and that SPL3 overexpressing plants, resistant to miR156 regulation, show a severe decrease in SPL7-mediated Cu deficiency responses. These include the expression of Cu-miRNAs and their targets and is probably due to competition between SPL7 and miR156-regulated SPL3 in binding to cis-regulatory elements in Cu-miRNA promoters. Thus, the conserved SPL7-mediated Cu-miRNA pathway could generally be affected by the miR156-SPL module, thereby underscoring the integration of the Cu-miRNA pathway with developmental and environmental stress responses in Arabidopsis thaliana.
Highlights
The deficiency of essential nutrients, such as copper (Cu), causes a decrease in agricultural productivity and crop performance
Medium (0 μM Cu) and MS supplemented with 100 μM BCS (100 BCS), 1 μM Cu (1 Cu) or 10 μM Cu (10 Cu) and the transcript levels were analyzed by Real-time quantitative PCR (RT-qPCR) (Figure 2)
In order to know whether the SPL3 expression under Cu deficiency is dependent on SPL7 through the effect on miR156, we examined SPL3 expression in 7-day-old WT
Summary
The deficiency of essential nutrients, such as copper (Cu), causes a decrease in agricultural productivity and crop performance. The absence of a functional MRE in a constitutive promoter-driven SPL3 transgene has allowed the miR156/157-independent expression of the SPL3 protein in transgenic plants. As a consequence, these plants showed a shortened juvenile phase and obtained an early flowering phenotype [16,17]. MiR398 expression, as well as its targets, suffer a diurnal oscillation at the transcriptional level [49] These data indicate that the spatiotemporal patterns of Cu-miRNA expression may have an important role in the response to nutrient deficiency and add another layer of complexity to the study of their function. Is there any evidence for the role of the miR156-SPL module in the regulation of the Cu deficiency responses during plant development? Second, is the Cu-miRNA pathway globally or influenced by developmental clues and by other abiotic stresses?
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