Biology subjects

Leyser, O.

Publications and source records attributed to Leyser, O..

6 recordsLinked to original sources

bioRxiv2025

A BRC1-modulated switch in auxin transport accounts for the competition between Arabidopsis axillary buds

As part of their modular development, plants continuously adapt their shoot branching architecture according to environmental conditions. This occurs by regulating the activity of axillary buds established in each leaf axil. Whether a bud grows into a shoot depends partly on the presence of other active shoots, which can inhibit bud activation. This systemic coordination is proposed to be mediated by the transport network of the plant hormone auxin, with buds competing to establish sustained transport of auxin, termed canalised auxin transport, into the main stem. A second hormone, strigolactone, tunes this competition by influencing the removal of the PIN1 auxin export protein from the plasma membrane, and hence the dynamics of canalisation. Strigolactone also regulates the expression of another key regulatory hub, the bud-expressed transcription factor BRANCHED1 (BRC1). The interplay between auxin transport and BRC1 in regulating bud activity is poorly understood. Here, we investigate this interplay in the context of competition between buds, using Arabidopsis explants with two axillary buds as a minimal system. Using experimental data, we develop a mathematical model of bud-bud competition in which BRC1 influences the establishment of canalised auxin transport by regulating the basal rate of auxin efflux in buds. We identify single model parameters that plausibly correspond to the dual impact of strigolactone on BRC1 expression and PIN1. We show that modulating these two parameters reproduces the dynamics of bud growth and bud-bud competition observed in relevant mutants and treatments. Our model produces testable hypotheses, which we validate by generating a chimeric PIN1 auxin transporter with impaired strigolactone sensitivity, helping us uncouple the effects of strigolactone on PIN1 and BRC1. These results support the hypothesis that BRC1 influences local bud competitiveness by tuning the basal rate of auxin efflux in buds. Together with the systemic feedbacks in the auxin transport network, this enables plants to adjust dynamically the number and location of growing branches.

plant biology↗

bioRxiv2024

Rapid evolution of gene expression patterns in flowering plants

Phenotypic differences between species are largely driven by changes in both protein-coding sequence and gene expression 1. The evolutionary history of angiosperms (flowering plants) is characterised by a highly accelerated rate of diversification, which Darwin referred to as an "abominable mystery" 2. Here we show, by analysing the transcriptomes from eight organs across seven species, that angiosperm protein-coding gene expression patterns evolve rapidly: within 45 million years, expression levels of orthologous genes diverged so strongly that they are more similar between different organs within a species than between what are considered homologous organs from different species. This finding differs from previous observations in mammals, which demonstrated that organ-dependent gene expression levels are largely conserved 3, 4, 5. Among the angiosperm organs, meristems and leaves show the highest degree of expression conservation, whereas stamen and pollen transcriptomes diverge rapidly. Examining changes in the expression level of functionally related genes, we found low rates for those involved in key cellular, metabolic and developmental processes. In contrast, particularly high rates were observed for genes that are involved in the response to endogenous and external stimuli, presumably reflecting an adaptive response of flowering plants to ever-changing environments. Our work reveals that the evolution of gene expression progresses at different rates in angiosperms and mammals, and provides a comprehensive resource to perform cross-kingdom comparative studies of transcriptome evolution.

plant biology↗

bioRxiv2021

KAI2 regulates seedling development by mediating light-induced remodelling of auxin transport

The photomorphogenic remodelling of seedling growth upon exposure to light is a key developmental transition in the plant life cycle. The /{beta}-hydrolase signalling protein KARRIKIN-INSENSITIVE2 (KAI2), a close homologue of the strigolactone receptor DWARF14 (D14), is involved in this process, and kai2 mutants have strongly altered seedling growth as a result1. KAI2 and D14 both act through the MAX2 (MORE AXILLARY BRANCHING2) F-box protein to target proteins of the SMAX1-LIKE (SUPPRESSOR OF MAX2 1) (SMXL) family for degradation, but the signalling events downstream of this step are unclear in both pathways2. Here, we show that kai2 phenotypes arise because of a failure to downregulate auxin transport from the seedling shoot apex towards the root system, rather than a failure to respond to light per se. We demonstrate that KAI2 controls the light-induced remodelling of the PIN-mediated auxin transport system in seedlings, promoting the reduction of PIN3, PIN4, and PIN7 abundance in older tissues, and the increase of PIN1, PIN2, PIN3, and PIN7 abundance in the root meristem, consistent with transition from elongation-mediated growth in the dark to meristematically-mediated growth in the light. We show that removing PIN3, PIN4 and PIN7 from kai2 mutants, or pharmacological inhibition of auxin transport and synthesis, is sufficient to suppress most kai2 seedling phenotypes. KAI2 is not required for the light-mediated changes in PIN gene expression but is required for the changes in PIN protein abundance at the plasma membrane; we thus propose that KAI2 acts to promote vesicle trafficking, consistent with previous suggestions about D14-mediated signalling in the shoot3.

plant biology↗

bioRxiv2020

Blocking plasmodesmata in specific phloem cell types reduces axillary bud growth in Arabidopsis thaliana

The plasticity of above ground plant architecture depends on the regulated re-activation and growth of axillary meristems laid down in the axils of leaves along the stem, which often arrest as dormant buds. Plasmodesmata connecting plant cells might control the movement of regulators involved in this developmental switch. Constructs capable of occluding these structures were employed in phloem cell types, because of the importance of phloem in local and systemic trafficking. We show that over-accumulation of callose within companion cells of the Arabidopsis inflorescence reduces the growth rates of activated buds, but does not affect bud activation. Growth rate reductions were not dependent on the phloem-mobile strigolactone receptor, which regulates bud activation. Furthermore, there was no correlation with early bud sugar profiles, which can also affect bud activity and depend on phloem-mediated delivery. It is therefore possible that an as yet unknown mobile signal is involved in modulating branch growth rate.

plant biology↗

bioRxiv2020

An ABA-GA bistable switch can account for natural variation in the variability of Arabidopsis seed germination time

Genetically identical plants growing in the same conditions can display heterogeneous phenotypes. Whether this phenotypic variability is functional and the mechanisms behind it are unclear. Here we use Arabidopsis seed germination time as a model system to examine phenotypic variability. We show extensive variation in seed germination time variability between Arabidopsis accessions, and use a multi-parent recombinant inbred population to identify two loci involved in this trait. Both loci include genes implicated in ABA signalling that could contribute to seed germination variability. Modelling reveals that the GA/ABA bistable switch underlying germination can amplify variability and account for the effects of these two loci on germination distributions. The model predicts the effects of modulating ABA and GA levels, which we validate genetically and by exogenous addition of hormones. We confirm that germination variability could act as a bet hedging strategy, by allowing a fraction of seeds to survive lethal stress.

plant biology↗

bioRxiv2016

Cross-species functional diversity within the PIN auxin efflux protein family

In Arabidopsis, development during flowering is coordinated by transport of the hormone auxin mediated by polar-localized PIN-FORMED1 (AtPIN1). However Arabidopsis has lost a PIN clade sister to AtPIN1, Sister-of-PIN1 (SoPIN1), which is conserved in flowering plants. We previously proposed that the AtPIN1 organ initiation and vein patterning functions are split between the SoPIN1 and PIN1 clades in grasses. Here we show that in the grass Brachypodium sopin1 mutants have organ initiation defects similar to Arabidopsis atpin1, while loss of PIN1 function in Brachypodium has little effect on organ initiation but alters stem growth. Heterologous expression of Brachypodium SoPIN1 and PIN1b in Arabidopsis provides further evidence of functional specificity. SoPIN1 but not PIN1b can mediate flower formation in null atpin1 mutants, although both can complement a missense allele. The behavior of SoPIN1 and PIN1b in Arabidopsis illustrates how membrane and tissue-level accumulation, transport activity, and interaction contribute to PIN functional specificity.

plant biology↗