Figure 1

Simplified rice-centric model of SL signaling in the regulation of shoot branching/tillering. SL degrades the D53 protein in rice^4,5 and the related SMXL6, SMXL7 and SMXL8 proteins in Arabidopsis¹. D53 directly prevents the transcriptional activation function of IPA1 (OsSPL14) in rice² and the related SPL3 and SPL17 proteins in wheat ⁸; D53 prevents IPA1 upregulation of D53 gene expression in rice², and TaSPL3 upregulation of TaTB1 gene expression in wheat⁸. IPA1 regulation of TB1 gene expression in rice has also been confirmed⁶ even though SL regulation of TB1 has not been reported in rice¹. TB1 can then inhibit shoot branching/tillering via unknown mechanisms⁷. miR156 integrates many environmental and endogenous signals¹¹ and post-transcriptionally regulates IPA1 gene expression³.