Do ArabidopsisSquamosa promoter binding Protein‐Likegenes act together in plant acclimation to copper or zinc deficiency?

Abstract

The genome of Arabidopsis thaliana encodes approximately 260 copper (Cu)‐dependent proteins, which includes enzymes in central pathways of photosynthesis, respiration and responses to environmental stress. Under Cu‐deficient growth conditions, Squamosa promoter binding Protein‐Like 7 ( SPL 7) activates the transcription of genes encoding Cu acquisition systems, and it mediates a metabolic reorganization to economize on Cu. The transcription factor SPL 7 groups among comparably large proteins in the SPL family, which additionally comprises a second group of small SPL proteins targeted by mi RNA 156 with roles in plant development. SPL 7 shares extended regions of sequence homology with SPL 1 and SPL 12. Therefore, we investigated the possibility of a functional overlap between these three members of the group of large SPL family proteins. We compared the spl1 spl12 double mutant and the spl1 spl7 spl12 triple mutant with both the wild type and the spl7 single mutant under normal and Cu‐deficient growth conditions. Biomass production, chlorophyll content and tissue elemental composition at the seedling stage, as well as plant and flower morphology during reproductive stages, confirmed the involvement of SPL 7, but provided no indication for important roles of SPL 1 or SPL 12 in the acclimation of Arabidopsis to Cu deficiency. Furthermore, we analyzed the effects of zinc (Zn) deficiency on the same set of mutants. Different from what is known in the green alga Chlamydomonas reinhardtii , Arabidopsis did not activate Cu deficiency responses under Zn deficiency, and there was no Cu overaccumulation in either shoot or root tissues of Zn‐deficient wild type plants. Known Zn deficiency responses were unaltered in spl7 , spl1 spl12 and spl1 spl7 spl12 mutants. We observed that CuZn SOD activity is strongly downregulated in Zn‐deficient A. thaliana , in association with an about 94% reduction in the abundance of the CSD 2 transcript, a known target of miR398. However, different from the known Cu deficiency responses of Arabidopsis, this Zn deficiency response was independent of SPL 7 and not associated with an upregulation of MIR 398b primary transcript levels. Our data suggest that there is no conservation in A. thaliana of the crosstalk between Zn and Cu homeostasis mediated by the single SPL family protein CRR 1 of Chl...

The Copper-microRNA Pathway Is Integrated with Developmental and Environmental Stress Responses in Arabidopsis thaliana

“…Although this hypothesis requires further experimental confirmation, competitive binding to GTAC motifs has been proposed for small SPL members in the case of reproductive development, causing substantial functional redundancy [27]. Functional redundancy between SPL1 and SPL12 has been also reported [34,35]. Importantly, whereas SPL7 binding results in transcriptional activation of target Cu deficiency genes, the occupancy of binding sites by SPL3 seems to inhibit their transcriptional activation, possibly due to differences in the interaction with other factors.…”

“…Among the large SPLs, the specific and unique role of SPL7 in Cu deficiency responses seems unquestioned. Function of the paralogous SPL1 and SPL12 genes could not be linked to the copper response [34], but rather seem to be implicated in thermotolerance [35], whereas spl14 mutants showed altered plant architecture [36].…”

Energy status-promoted growth and development of Arabidopsis require copper deficiency response transcriptional regulator SPL7

“…Our standard greenhouse soil is Cu-deficient (low Cu), and the defects in reproduction of spl7-1 are rescued by watering with 2 mM CuSO 4 (control) once per week (Schulten et al, 2019). With this supplementation, Cu concentrations in rosette leaf and aerial tissues of spl7-1 were significantly higher than in unamended low-Cu soil (Figure 5B), and the stunted growth of spl7-1 was partially rescued (Figure 5C), as was reported earlier (Yamasaki et al, 2009;Bernal et al, 2012;Garcia-Molina et al, 2014a;Yan et al, 2017).…”

“…Soil cultivation was in 16-h long days (145 µmol m -2 s -1 , 22°C)/8-h night (18°C), with Cu conditions as described (Schulten et al, 2019). Glass petri dishes were soaked in 0.…”

“…With the exception of SPL7, the biological functions of subfamily I SPL proteins are less well understood (Stone et al, 2005;Chao et al, 2017;Schulten et al, 2019).…”