Auxin acts independently of DELLA proteins in regulating gibberellin levels

The effect of auxins, such as indole-3-acetic acid, is at least in part mediated by its effect on GA metabolism,6 since auxin upregulates biosynthesis genes such as GA 3-oxidase and GA 20-oxidase and downregulates GA catabolism genes such as GA 2-oxidases, leading to elevated levels of bioactive GA1.7 In our recent paper,1 we have provided evidence that this action of IAA is largely independent of DELLA proteins, the negative regulators of GA action,8,9 since the auxin effects are still present in the DELLA-deficient la cry-s genotype of pea

James B. Reid; Sandra E. Davidson; John J. Ross

2011

Scholarcy highlights

  • Shoot elongation is a vital process for plant development and productivity, in both ecological and economic contexts
  • The effect of auxins, such as indole-3-acetic acid, is at least in part mediated by its effect on GA metabolism, since auxin upregulates biosynthesis genes such as GA 3-oxidase and GA 20-oxidase and downregulates GA catabolism genes such as GA 2-oxidases, leading to elevated levels of bioactive GA1.7 In our recent paper, we have provided evidence that this action of IAA is largely independent of DELLA proteins, the negative regulators of GA action, since the auxin effects are still present in the DELLA-deficient la cry-s genotype of pea
  • Our recent results, in themselves, do not show the generality of the auxin-GA relationship across species and phylogenetic groups or across different tissue types and responses. They do not touch on the ecological benefits of the auxin-GA interaction
  • With respect to GA1 synthesis, the shoot-expressed GA20ox gene seems to be only marginally upregulated in pea shoots, with the main effect attributable to the upregulation of Mendel’s GA 3-oxidase gene, LE
  • In roots the auxin action inhibitor PCIB caused significantly less inhibition of elongation in la cry-s plants than in phenotypically wild type plants, this does not distinguish between the effect of auxin on GA synthesis or an effect on the GA response pathway
  • We suggest it is preferable to deplete auxin using auxin transport inhibitors, decapitation or excised segments
  • With multi-gene families involved with both processes and auxin sometimes regulating members of these families in opposite directions, metabolism studies are the only easy method for summing the actions of the gene family at the metabolite level, as was done in O’Neill et al

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