Walker, C. H. | bioRxiv Science

bioRxiv2019

Auxin export from proximal fruits drives arrest in competent inflorescence meristems

A well-defined set of regulatory pathways control entry into the reproductive phase in flowering plants [1]. Conversely, little is known about the mechanisms that control the end of the reproductive phase ( floral arrest), despite this being a critical process for optimising fruit and seed production. Complete fruit removal or lack of fertile fruit-set in male sterile mutants, for example male sterile1 (ms1), prevents timely floral arrest in the model plant Arabidopsis [2]. These observations formed the basis for Hensel and colleagues model in which end-of-flowering was proposed to result from a cumulative fruit/seed-derived signal that caused simultaneous global proliferative arrest (GPA) in all inflorescences [2]. Recent studies have suggested that end-of-flowering involves gene expression changes at the floral meristem which are at least in part controlled by the FRUITFULL-APETELA2 pathway [3,4], however there is limited understanding of how this process is controlled and the communication needed at the whole plant level. Here, we provide new information providing a framework for the fruit-to-meristem (F-M) communication implied by the GPA model [5]. We show that floral arrest in Arabidopsis is not global and does not occur synchronously between branches, but rather that the arrest of each inflorescence is a local process, driven by auxin export from fruit proximal to the inflorescence meristem (IM). Furthermore, we show that inflorescence meristems are only competent for floral arrest once they reach a certain developmental age. Understanding the regulation of floral arrest is of major importance for the future manipulation of flowering to extend and maximise crop yields.

plant biology↗

bioRxiv2019

Root density sensing allows pro-active modulation of shoot growth to avoid future resource limitation

Plants use environmental cues to determine their optimal root and shoot growth. It is well known to gardeners and horticulturists alike that soil volume - most commonly in the form of pot size - strongly restricts plant growth, but the mechanisms by which this effect occurs remain unclear. Here, we show that shoot growth scales directly with soil volume, independently of the nutritional content of the soil, and that plants can become volume restricted even in the presence of abundant resources. We show that plants can detect their soil volume as early as 3 weeks post germination, and that shoot growth restriction therefore constitutes a pro-active decision by the plant to avoid resource limitation later in the life cycle. Shoot growth restriction is not directly linked to root growth restriction, and does not occur in response to the mechanical detection of the pot walls. Rather, we show that plants detect their soil volume by detecting the density of roots in the proximity of their root system. As such, volume restriction may be intimately connected with the mechanism by which plants sense and respond to the roots of other plants in the rhizosphere. Our work demonstrates the remarkable ability of plants to make pro-active decisions about their growth to ensure they can complete their cycle, and has important implications for agricultural practise regarding both nutrient use efficiency and yield.

plant biology↗