Connective auxin transport contributes to strigolactone-mediated shoot branching control independent of the transcription factor BRC1
Fig 9
Cartoon of a nodal Arabidopsis stem segment with associated bud (leaf not shown). The coloured arrows indicate the flow of auxin (green) and strigolactone (red). The blue shading indicates the polar auxin transport stream (PATS), with PIN1 dominating, and the orange shading represents the connective auxin transport (CAT), with PIN3, PIN4 and PIN7 dominating. The black lines indicate hypotheses involving either promotion (arrowheads) or repression (end lines). Specifically, we have previously proposed that positive feedback between auxin flux and PIN polarisation drives canalisation of auxin transport between the bud and the main stem, and this is necessary for sustained bud activation. We have also previously proposed that strigolactone inhibits canalisation by triggering PIN1 endocytosis. Data presented here suggest that this might also be true for PIN7, but that the transport activities of PIN3, PIN4 and PIN7 are all important to allow maximal bud activation in strigolactone-defective mutants. Although it is possible that ABCB transporters are also important in the stem, the very different effects of the abcb19 mutant compared to the pin347 triple mutant lead us to propose that an important site of action is in the bud, where they may contribute to auxin loading, and therefore canalisation of auxin transport out of the bud. Consistent with this idea, the branchy phenotype of brc1 mutants is partly suppressed in the abcb19 mutant background. This is consistent with the idea that BRC1 acts at least in part through increasing bud auxin loading, either independently of upstream of ABCB19.
doi: https://doi.org/10.1371/journal.pgen.1008023.g009