Cytokinin and reproductive shoot architecture: bigger and better?

Cytokinin (CK) is a key plant hormone, but one whose effects are often misunderstood, partly due to reliance on older data from before the molecular genetic age of plant science. In this mini-review, we examine the role of CK in controlling the reproductive shoot architecture of flowering plants. We begin with a long overdue re-examination of the role of CK in shoot branching, and discuss the relatively paucity of genetic evidence that CK does play a major role in this process.

FLOWERING LOCUS T-mediated thermal signalling regulates age-dependent inflorescence development in Arabidopsis thaliana.

Many plants show strong heteroblastic changes in the shape and size of organs as they transition from juvenile to reproductive age. Most attention has been focused on heteroblastic development in leaves, but we wanted to understand heteroblastic changes in reproductive organ size. We therefore studied the progression of reproductive development in the model plant Arabidopsis thaliana, and found strong reductions in the size of flowers, fruit, seed, and internodes during development.

FLOWERING LOCUS T mediates photo-thermal timing of inflorescence meristem arrest in Arabidopsis thaliana.

Plants integrate environmental information into their developmental program throughout their lifetime. Light and temperature are particularly critical cues for plants to correctly time developmental transitions. Here, we investigated the role of photo-thermal cues in the regulation of the end-of-flowering developmental transition in the model plant Arabidopsis (Arabidopsis thaliana).

Just enough fruit: understanding feedback mechanisms during sexual reproductive development.

The fruit and seed produced by a small number of crop plants provide the majority of food eaten across the world. Given the growing global population, there is a pressing need to increase yields of these crops without using more land or more chemical inputs. Many of these crops display prominent 'fruit-flowering feedbacks', in which fruit produced early in sexual reproductive development can inhibit the production of further fruit by a range of mechanisms.

Cytokinin signaling regulates two-stage inflorescence arrest in Arabidopsis.

To maximize reproductive success, flowering plants must correctly time entry and exit from the reproductive phase. While much is known about mechanisms that regulate initiation of flowering, end-of-flowering remains largely uncharacterized. End-of-flowering in Arabidopsis (Arabidopsis thaliana) consists of quasi-synchronous arrest of inflorescences, but it is unclear how arrest is correctly timed with respect to environmental stimuli and reproductive success.

Integrated dominance mechanisms regulate reproductive architecture in Arabidopsis thaliana and Brassica napus.

The production of seed in flowering plants is complicated by the need to first invest in reproductive shoots, inflorescences, flowers, and fruit. Furthermore, in many species, it will be months between plants generating flowers and setting seed. How can plants therefore produce an optimal seed-set relative to environmental resources when the "reproductive architecture" that supports seed-set needs to be elaborated so far in advance? Here, we address this question by investigating the spatio-temporal control of reproductive architecture in Arabidopsis (Arabidopsis thaliana) and Brassica napus.

Wheat plants sense substrate volume and root density to proactively modulate shoot growth.

Plants must carefully coordinate their growth and development with respect to prevailing environmental conditions. To do this, plants can use a range of nutritional and non-nutritional information that allows them to proactively modulate their growth to avoid resource limitations. As is well-known to gardeners and horticulturists alike, substrate volume strongly influences plant growth, and maybe a key source of non-nutritional information for plants.

Bloom and bust: understanding the nature and regulation of the end of flowering.

The reproduction of flowering plants is an incredibly important process, both ecologically and economically. A huge body of work has examined the mechanisms by which flowering plants correctly time their entry into the reproductive phase (the 'floral transition'). However, the corresponding mechanisms by which plants exit the reproductive phase remain relatively neglected.

Auxin export from proximal fruits drives arrest in temporally competent inflorescences.

A well-defined set of regulatory pathways control entry into the reproductive phase in flowering plants, but little is known about the mechanistic control of the end-of-flowering despite this being a critical process for optimization of fruit and seed production. Complete fruit removal, or lack of fertile fruit-set, prevents timely inflorescence arrest in Arabidopsis, leading to a previous proposal that a cumulative fruit/seed-derived signal causes simultaneous 'global proliferative arrest'. Recent studies have suggested that inflorescence arrest involves gene expression changes in the inflorescence meristem that are, at least in part, controlled by the FRUITFULL-APETALA2 pathway; however, there is limited understanding of how this process is coordinated at the whole-plant level.

Strigolactone synthesis is ancestral in land plants, but canonical strigolactone signalling is a flowering plant innovation.

Background: Strigolactones (SLs) are an important class of carotenoid-derived signalling molecule in plants, which function both as exogenous signals in the rhizosphere and as endogenous plant hormones. In flowering plants, SLs are synthesized by a core pathway of four enzymes and are perceived by the DWARF14 (D14) receptor, leading to degradation of SMAX1-LIKE7 (SMXL7) target proteins in a manner dependent on the SCF ubiquitin ligase. The evolutionary history of SLs is poorly understood, and it is not clear whether SL synthesis and signalling are present in all land plant lineages, nor when these traits evolved.

A distributive '50% rule' determines floral initiation rates in the Brassicaceae.

The spatio-temporal production of flowers is key to determining reproductive fitness in most flowering plants and yield in many crop species, but the mechanisms regulating this 'reproductive architecture' are poorly characterized. Here, we show that in members of the Brassicaceae, total flower number is largely independent of inflorescence number and that the proportion of flowers initiated on the secondary inflorescences represents ~50% of total floral production, irrespective of secondary inflorescence number. This '50% rule' acts as a coordinating principle for reproductive development in Brassicaceae, and similar principles may operate in other species.

Phytochrome A Mediates Blue-Light Enhancement of Second-Positive Phototropism in Arabidopsis.

Hypocotyl phototropism of etiolated Arabidopsis seedlings is primarily mediated by the blue-light receptor kinase phototropin 1 (phot1). Phot1-mediated curvature to continuous unilateral blue light irradiation (0.5 μmol m(-2) s(-1)) is enhanced by overhead pre-treatment with red light (20 μmol m(-2) s(-1) for 15 min) through the action of phytochrome (phyA).