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

Abstract

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 branch-ing 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- functionmutation 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 phen-ocopied 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.

Keywords

tree architecture; branching modeling; strigolactones; auxin distribution; Betulapendula

Published in

Proceedings of the National Academy of Sciences of the United States of America
2013, volume: 120, number: 48, article number: e2308587120

SLU Authors

• Ljung, Karin

  • Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences
    

Global goals (SDG)

SDG7 Affordable and clean energy
SDG13 Climate action

UKÄ Subject classification

Developmental Biology
Botany

Publication identifier

• DOI: https://doi.org/10.1073/pnas.2308587120

Permanent link to this page (URI)

https://res.slu.se/id/publ/128345