Tree architecture: A strigolactone-deficient mutant reveals a connection between branching order and auxin gradient along the tree stem

Chang Su, Andrzej Kokosza, Xiaonan Xie, Aleš Pěnčík, Youjun Zhang, Pasi Raumonen, Xueping Shi, Sampo Muranen, Melis Kucukoglu Topcu, Juha Immanen, Risto Hagqvist, Omid Safronov, Juan Alonso-Serra, Gugan Eswaran, Mirko Pavicic Venegas, Karin Ljung, Sally Ward, Ari Pekka Mähönen, Kristiina Himanen, Jarkko SalojärviAlisdair R. Fernie, Ondřej Novák, Ottoline Leyser, Wojtek Pałubicki, Ykä Helariutta, Kaisa Nieminen

Research output: Contribution to journalArticleScientificpeer-review


Due to their long lifespan, trees and bushes develop higher order of branches in a perennial manner. In contrast to a tall tree, with a clearly defined main stem and branching order, a bush is shorter and has a less apparent main stem and branching pattern. To address the developmental basis of these two forms, we studied several naturally occurring architectural variants in silver birch (Betula pendula). Using a candidate gene approach, we identified a bushy kanttarelli variant with a loss-of-function mutation in the BpMAX1 gene required for strigolactone (SL) biosynthesis. While kanttarelli is shorter than the wild type (WT), it has the same number of primary branches, whereas the number of secondary branches is increased, contributing to its bush-like phenotype. To confirm that the identified mutation was responsible for the phenotype, we phenocopied kanttarelli in transgenic BpMAX1::RNAi birch lines. SL profiling confirmed that both kanttarelli and the transgenic lines produced very limited amounts of SL. Interestingly, the auxin (IAA) distribution along the main stem differed between WT and BpMAX1::RNAi. In the WT, the auxin concentration formed a gradient, being higher in the uppermost internodes and decreasing toward the basal part of the stem, whereas in the transgenic line, this gradient was not observed. Through modeling, we showed that the different IAA distribution patterns may result from the difference in the number of higher-order branches and plant height. Future studies will determine whether the IAA gradient itself regulates aspects of plant architecture.

Original languageEnglish
Article numbere2308587120
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number48
Publication statusPublished - 2023
MoE publication typeA1 Journal article-refereed

Fields of Science

  • auxin distribution
  • Betula pendula
  • branching modeling
  • strigolactones
  • tree architecture
  • 11831 Plant biology

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