Biology subjects

Spencer, V.

Publications and source records attributed to Spencer, V..

3 recordsLinked to original sources

bioRxiv2025

The cytochrome P450 enzyme MpCYP78E1 inhibits meristem initiation and activity in Marchantia polymorpha

Plant shoot branches are formed by the initiation and activation of generative centres known as meristems. In dichotomously branching plants, such as many bryophytes and lycophytes, new meristems are formed when a pre-existing meristem splits into two daughter meristems. These meristems may be active and produce shoot branches or may be inactive. Here, we show that in conditions where meristem inactivation occurs, such as simulated shade, the position of the inactive meristem alternated between either side of the plant body in the liverwort Marchantia polymorpha. Using this predictable pattern, we generated transcriptomes of active and inactive meristems and identified the cytochrome P450 monooxygenase, MpCYP78E1, as a novel regulator of meristem activity. MpCYP78E1 reporter expression was higher in active meristems than inactive meristems. More meristems were active in loss of function mutants than wild type, and fewer meristems were active in gain of function mutants, indicating that MpCYP78E1 inhibits meristem activity. Furthermore, unlike wild type, Mpcyp78e1 loss of function mutants produced supernumerary meristem from the centre of the mature plant body. We conclude that MpCYP78E1 inhibits both meristem initiation and activity to modulate shoot branching architecture.

plant biology↗

bioRxiv2024

The three-dimensional anatomy and dorsoventral asymmetry of the mature Marchantia polymorpha meristem develops from a symmetrical gemma meristem

Meristems are three-dimensional generative structures that maintain a population of stem cells whilst producing new organs and tissues. Meristems develop in all land plants, however we know relatively little about the spatial and temporal regulation of meristem structure in lineages such as the bryophytes. Here we describe the three-dimensional anatomy of the meristem during the development of the liverwort, Marchantia polymorpha. Using optical reconstructions of the frontal, sagittal and transverse planes through the mature meristem, we show that the apical stem cell is sub-apical, ventral, and located in the outer cell layer. The anatomy of the mature meristem is therefore asymmetrical in the dorsoventral axis, which is reflected by the domain specific protein localisation of Marchantia Class III and Class IV Homeodomain-Leucine-Zippers (MpC3HDZ and MpC4HDZ) and promoter activity of MpYUCCA2. The dorsoventral asymmetry that defines the mature meristem is absent in the juvenile meristems of the asexual propagules known as gemmae. We discovered that anatomical dorsoventral asymmetry of the meristem forms after two days of gemmaling growth and is accompanied by expression of the dorsal identity reporter, MpC3HDZ. We conclude that the gemma meristem is in a state of arrested development and undergoes anatomical rearrangement to develop the three-dimensional meristem structure of the mature plant.

plant biology↗

bioRxiv2022

Diverse branching forms regulated by a core auxin transport mechanism in plants

Diverse branching forms have evolved multiple times across the tree of life to facilitate resource acquisition and exchange with the environment. In land plants, sporophyte branching enabled the diversification of the dominant vascular plant clade and arose in their last shared common ancestor; the bryophyte sisters to vascular plants are unbranched. Mechanisms for sporophyte branching are well known in Arabidopsis, where branch initiation and plastic branch outgrowth require directional auxin transport by PIN proteins. However, no broadly applicable genetic mechanisms for branching in vascular plants are known. We have used a combination of surgical and pharmacological treatments and PIN expression analyses in the lycophyte Selaginella kraussiana to identify PIN-mediated auxin transport as the ancestral mechanism for branching within vascular plants. We show that shortrange auxin transport out of the shoot tips promotes branching, and that branch dominance is coordinated by long-range auxin transport throughout the shoot system. Moreover, the plastic outgrowth of a branch from a unique organ system innovated in lycophytes (the rhizophore) is regulated by long-range auxin transport and associated with a transitory drop in PIN expression. We conclude that an ancestral mechanism for branching was independently recruited into plastic branch outgrowth in lycophytes and seed plants. Considered in conjunction with data from other species, our results highlight a pivotal role for the co-option of PINs into the evolution of branching in diverse plant forms.

plant biology↗