A SQUAMOSA PROMOTER BINDING PROTEIN, LeSPL-CNR targeted by SlymiR157
negatively regulates Fe deficiency response in tomato roots
Iron (Fe) homeostasis is critical for plant growth, development and
stress response, which is tightly controlled by intricated regulatory
networks in which transcription factors (TFs) play a central role.
Whilst a series of basic helix-loop-helix (bHLH) TFs have been
functionally characterized to contribute to Fe homeostasis, regulatory
layers beyond bHLH TFs remain largely unclear. Here, we demonstrate that
a SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) TF, LeSPL-CNR, negatively
regulates Fe deficiency responses in tomato roots. Fe deficiency rapidly
repressed the expression of LeSPL-CNR. However, Fe-deficiency-responses
were intensified in two LeSPL-CNR CRISPR/Cas9 gene editing transgenic
lines compared with wild-type plants. By comparative transcriptome
analyses, we identified 47 Fe-deficiency responsive genes including
SlbHLH101 whose expression were negatively regulated by LeSPL-CNR.
LeSPL-CNR is localized to nucleus and yeast one-hybrid and luciferase
reporter assays revealed that LeSPL-CNR could interact with GTAC motif
and BOX4 motif of SlbHLH101 promoter to repress its expression.
Moreover, Fe deficiency-induced expression inhibition of LeSPL-CNR is
correlated well with SlymiR157 expression induction. Additionally,
transgenic tomato overexpressing SlymiR157 displayed improved Fe
deficiency responses similar to that of LeSPL-CNR loss-of-function
mutants. Altogether, we propose that miR157-LeSPL-CNR module provided an
additional pathway that acts upstream of SlbHLH101 to regulate Fe
homeostasis in tomato roots.