# A space for time. Exploring temporal regulation of plant development across spatial scales

## TL;DR

This paper reviews how plant development is regulated over time, from whole-plant processes to cell-level changes, and explores the mechanisms controlling these transitions.

## Contribution

The paper systematically reviews temporal regulation of plant development across spatial scales, highlighting gaps and mechanisms.

## Key findings

- Developmental timing in plants is tightly regulated at the whole-organism scale, including germination, flowering, and senescence.
- Cell-level transitions in plants are also temporally regulated, though less is known about the specific mechanisms.
- Environmental and cellular factors like temperature, photoperiod, and tissue context influence developmental timing.

## Abstract

Plants continuously undergo change during their life cycle, experiencing dramatic phase transitions altering plant form, and regulating the assignment and progression of cell fates. The relative timing of developmental events is tightly controlled and involves integration of environmental, spatial, and relative age‐related signals and actors. While plant phase transitions have been studied extensively and many of their regulators have been described, less is known about temporal regulation on a smaller, cell‐level scale. Here, using examples from both plant and animal systems, we outline time‐dependent changes. Looking at systemic scale changes, we discuss the timing of germination, juvenile‐to‐adult transition, flowering, and senescence, together with regeneration timing. Switching to temporal regulation on a cellular level, we discuss several instances from the animal field in which temporal control has been examined extensively at this scale. Then, we switch back to plants and summarize examples where plant cell‐level changes are temporally regulated. As time cannot easily be separated from signaling derived from the environment and tissue context, we next discuss factors that have been implicated in controlling the timing of developmental events, reviewing temperature, photoperiod, nutrient availability, as well as tissue context and mechanical cues on the cellular scale. Afterwards, we provide an overview of mechanisms that have been shown or implicated in the temporal control of development, considering metabolism, division control, mobile signals, epigenetic regulation, and the action of transcription factors. Lastly, we look at remaining questions for the future study of developmental timing in plants and how recent technical advancement can enable these efforts.

Developmental timing in plants is tightly regulated at the whole‐organism scale, from germination to flowering. Less is known about when and how local transitions are temporally regulated. Not every cell or tissue change happens at any time, and by now, several examples are known where there appears to be regulation of the timing of these decisions. In this review, we explore examples of developmental transitions whose timing is being controlled and the underlying mechanisms.