Biology subjects

Plackett, A. R. G.

Publications and source records attributed to Plackett, A. R. G..

8 recordsLinked to original sources

bioRxiv2026

Characteristics of the C4 bundle sheath emerge in C3 rice after editing a plasma membrane proton ATPase

C4 photosynthesis improves light, water and nitrogen-use efficiencies and can raise yield by 50% compared with the ancestral C3 pathway. Engineering C4 traits into C3 crops could substantially boost food production but requires coordinated modifications to leaf anatomy and cell-specific photosynthetic function. For example, C4 leaves contain more numerous, shorter bundle sheath cells that are photosynthetically active. In searching for transcriptional regulators of bundle sheath development in C3 rice, we unexpectedly found OSA3, a plasma membrane H+-ATPase that is expressed in bundle sheath cells as they elongate, and when knocked out reduces their length due to reduced apoplastic acidification. Bundle sheath cell number and chloroplast occupancy are increased. Thus, switching between C3 and C4 bundle sheath identity is controlled by acid growth, and OSA3 represents a simple tool for C4 engineering.

plant biology↗

bioRxiv2025

Transgenerational polarity axis inheritance during Ceratopteris embryogenesis

For sexually reproducing organisms to pass on their genetic information, progeny must successfully establish. Various life history strategies have evolved, using either dispersal of large numbers of progeny or intensive nurturing of a few. Most plants use the former strategy, but ferns generate a single embryo in the exact same location as the mother, and it is unknown how progeny success is promoted, or how embryogenesis is adapted. By studying Ceratopteris richardii embryogenesis, we find that maternal tissues guide orientation of the early embryo body axis, thus aligning its root pole towards the homologous maternal rhizoids. We find that axis polarity inheritance is mediated by maternal tissue mechanical patterns, and thus identify a robust mechanism for progeny establishment as a nurturing strategy in plants.

plant biology↗

bioRxiv2025

LEAFY demonstrates ancestral reproductive functions in the gametophyte and not the sporophyte of the fern Ceratopteris richardii

Flowers are a key reproductive innovation of the angiosperms. They evolved as a modification of the ancestral plant life cycle whereby the haploid gamete-producing generation (gametophyte) became enclosed within the diploid, spore-producing generation (sporophyte). The transcription factor LEAFY (LFY) initiates angiosperm floral development, yet its lineage predates flowers and is found across all land plants. LFY function outside angiosperms is known from the moss Physcomitrium patens, where they control the first division of the sporophyte, and from the model fern Ceratopteris richardii, a vascular plant without seeds or flowers, where CrLFY1 and CrLFY2 maintain vegetative meristem activity. However, how LFYs reproductive role evolved remains unclear. Using over-expression, we uncover new roles for CrLFY1/2 in fern gametophyte reproduction, particularly in sperm cells and in the gametophytes multicellular notch meristem. No sporophytic reproductive function was detected, but over-expression supports a role in fern frond compounding and a conserved role in the zygotes first division. Our findings highlight an ancestral LFY function in fern haploid-stage reproduction, which may have been co-opted into the sporophyte during the origin of the flower. Summary StatementThe origin of LEAFYs floral function is unknown, with only vegetative roles known from seedless plants. We identify ancestral reproductive roles for the first time, unexpectedly in the fern gametophyte.

developmental biology↗

bioRxiv2025

Gene networks are conserved across reproductive development between the fern Ceratopteris richardii and the flowering plant Arabidopsis thaliana

How plants first invented seeds is a longstanding unresolved evolutionary question. Seed-bearing plants arose from within seedless vascular plants, with ferns as their closest relatives, but how the seed developmental programme first originated has remained intractable through comparative morphology or the fossil record. To investigate this question at the level of gene network evolution, we established a transcriptional expression atlas across sporophyte and gametophyte reproductive development of the fern Ceratopteris richardii and compared reproductive-associated genes to those of Arabidopsis thaliana. Conservation was detected between distinct organs. As in flowering, the hormone gibberellin promoted sporing of the fern sporophyte shoot. Sporophyll genes were conserved with floral development. Gametophyte post-fertilization egg chamber (archegonium) genes were conserved with both pre- and post-fertilization seed development, as were two post-fertilization signals, auxin and sugar. We conclude that the seed may first have arisen through the mis-expression of archegonium developmental programmes within the developing sporophyte sporangium.

plant biology↗

bioRxiv2024

Increased chloroplast area in the rice bundle sheath through cell specific perturbation of brassinosteroid signalling

In the leaves of C3 species such as rice, mesophyll cells contain the largest compartment of photosynthetically active chloroplasts. In contrast, plants that use the derived and more efficient C4 photosynthetic pathway have a significant chloroplast compartment in both bundle sheath and mesophyll cells. Accordingly, the evolution of C4 photosynthesis from the ancestral C3 state requires an increase in the chloroplast compartment of the bundle sheath. Here we investigated the potential to increase chloroplast compartment size in rice bundle sheath cells by manipulating brassinosteroid signalling. Treatment with brassinazole, a brassinosteroid biosynthesis inhibitor, increased leaf chlorophyll content and increased the number but decreased the area of chloroplasts in bundle sheath cells. Constitutive overexpression of the BRASSINAZOLE RESISTANT 1 (OsBZR1) transcription factor increased bundle sheath chloroplast area by up to 45% but plants became chlorotic. However, when OsBZR1 was placed under the control of a bundle sheath specific promoter, the negative effects on growth and viability were removed whilst chloroplast area still increased. In summary, we report a role for brassinosteroids in controlling chloroplast area and number in rice and conclude that cell-specific manipulation of brassinosteroid signalling can be used to manipulate the chloroplast compartment in rice bundle sheath cells.

plant biology↗

bioRxiv2023

Delayed exposure of rice to light partially phenocopies C4 bundle sheath characteristics by reducing cell length

C4 photosynthesis has arisen in over sixty lineages of angiosperms. Despite significant variation in characteristics of the C4 leaf, in all cases a compartment rich in chloroplasts allows high concentrations of CO2 to be supplied to RuBisCO. In most C4 lineages this is associated with increased chloroplast content of bundle sheath cells. As characteristics of C4 leaves are derived from processes operating in the ancestral C3 state, we studied greening of the bundle sheath in C3 rice. Total visible chloroplast area in bundle sheath and mesophyll cells was similar but the larger volume of bundle sheath cells reduced the proportion of cell occupied by chloroplast, and the longest bundle sheath cells had the lowest chloroplast content. Application of exogenous cytokinin and gibberellin increased chloroplast content of the longest bundle sheath cells but did not change cell shape. In contrast, delayed exposure to light reduced the number of very long bundle sheath cells but increased leaf length indicating delayed exit from the cell cycle. We conclude that in the C3 state, the plant hormones cytokinin and gibberellin are regulators of the bundle sheath cell-chloroplast relationship and that final bundle sheath length is affected by light-mediated control of exit from the cell cycle. HighlightExtended darkness can reduce maximum bundle sheath cell length in rice and hormones condition the set-point between cell size and chloroplast content.

plant biology↗

bioRxiv2021

Conditional Stomatal Closure in a Fern Shares Molecular Features with Flowering Plant Active Stomatal Responses

Stomata evolved as plants transitioned from water to land, enabling carbon dioxide uptake and water loss to be controlled. In flowering plants, the most recently divergent land plant lineage, stomatal pores actively close in response to drought. In this response, the phytohormone abscisic acid (ABA) triggers signalling cascades that lead to ion and water loss in the guard cells of the stomatal complex, causing a reduction in turgor and pore closure. Whether this stimulus-response coupling pathway acts in other major land plant lineages is unclear, with some investigations reporting that stomatal closure involves ABA but others concluding that closure is passive. Here we show that in the model fern Ceratopteris richardii active stomatal closure is conditional on sensitisation by pre-exposure to either low humidity or exogenous ABA and is promoted by ABA. RNA-seq analysis and de novo transcriptome assembly reconstructed the protein coding complement of the C. richardii genome with coverage comparable to other plant models, enabling transcriptional signatures of stomatal sensitisation and closure to be identified. In both cases, changes in abundance of homologs of ABA, Ca2+ and ROS-related signalling components were observed, suggesting that the closure response pathway is conserved in ferns and flowering plants. These signatures further suggested that sensitisation is achieved by lowering the threshold required for a subsequent closure-inducing signal to trigger a response. We conclude that the canonical signalling network for active stomatal closure functioned in at least a rudimentary form in the stomata of the last common ancestor of ferns and flowering plants. Significance StatementStomata are valve-like pores that control the uptake of CO2 and the loss of water vapour in almost all land plants. In flowering plants, stomatal opening and closure is actively regulated by a stimulus-response coupling network. Whether active stomatal responses are present in other land plant lineages such as ferns has been hotly debated. Here we show that stomatal responses in the fern Ceratopteris richardii are active but depend on their past growth environment, and demonstrate that fern stomatal closure and sensitisation are associated with the altered expression of genes whose homologs function in the canonical stomatal regulatory network of flowering plants. Genetic pathways for active stomatal regulation therefore most likely evolved before the divergence of ferns and flowering plants.

plant biology↗

bioRxiv2018

LEAFY maintains apical stem cell activity during shoot development in the fern Ceratopteris richardii

During land plant evolution, determinate spore-bearing axes (retained in extant bryophytes such as mosses) were progressively transformed into indeterminate branching shoots with specialized reproductive axes that form flowers. The LEAFY transcription factor, which is required for the first zygotic cell division in mosses and primarily for floral meristem identity in flowering plants, may have facilitated developmental innovations during these transitions. Mapping the LEAFY evolutionary trajectory has been challenging, however, because there is no functional overlap between mosses and flowering plants, and no functional data from intervening lineages. Here, we report a transgenic analysis in the fern Ceratopteris richardii that reveals a role for LEAFY in maintaining cell divisions in the apical stem cells of both haploid and diploid phases of the lifecycle. These results support an evolutionary trajectory in which an ancestral LEAFY module that promotes cell proliferation was progressively co-opted, adapted and specialized as novel shoot developmental contexts emerged.

plant biology↗