ABSTRACT

Being continuously exposed to variable environmental conditions, plants produce phytohormones to react quickly and specifically to these changes. The phytohormone ethylene is produced in response to multiple stresses. While the role of ethylene in defense responses to pathogens is widely recognized, recent studies in Arabidopsis and crop species highlight an emerging key role for ethylene in the regulation of organ growth and yield under abiotic stress. Molecular connections between ethylene and growth-regulatory pathways have been uncovered, and altering the expression of ethylene response factors (ERFs) provides a new strategy for targeted ethylene-response engineering. Crops with optimized ethylene responses show improved growth in the field, opening new windows for future crop improvement. This review focuses on how ethylene regulates shoot growth, with an emphasis on leaves.

Adapting Plant Growth to the Environment: Why and How?

The sessility of plants is undoubtedly their most disadvantageous feature compared to other living organisms, and implies that their survival can be threatened by environmental perturbations. However, plants have developed fascinating mechanisms enabling rapid detection of changing conditions accompanied by highly complex molecular responses, resulting in remarkable phenotypic plasticity. During the vegetative growth stage, one tightly controlled process is plant growth. Under favorable conditions, root and shoot growth is crucial to enable continuous nutrient uptake and energy production through photosynthesis, respectively. Leaf growth, for example, is controlled by no less than six different cellular mechanisms, including precise orchestration of the switch between cell division, that drives the growth of very young leaf primordia, and cell expansion and differentiation (reviewed in [1]). By contrast, sustaining growth under unfavorable conditions could be detrimental. For example, growth under drought stress would increase the evaporative surface of the plant, rendering the plant even more susceptible. Plants thus constantly evaluate whether the environmental signals are favorable for growth or not, and redirect their resources either for growth or for stress defense.

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