Growth arrest is a DNA damage protection strategy in Arabidopsis

Introduction

The growth-defense trade-off, characterized by the simultaneous restriction of growth and activation of defense mechanisms in response to environmental threats, is observed in diverse organisms, from microbes to plants and mammalian cells^{1, 2–3}. This trade-off is often attributed to competition for shared resources along the growth and defense pathways⁴. For example, yeast cells prioritize the production of defense proteins by repressing transcripts related to cell division during acute stress⁵.

Although plants possess cell-autonomous checkpoints for stress-dependent control of cell division that are equivalent to those described in microorganisms and mammalian cell cultures⁶, the growth-defense trade-off results in a systemic growth arrest. Recent studies challenge the view that the trade-off is caused by simple ‘metabolic competition’ and show that it results from a programmed interaction between cellular signaling pathways^7,8. In a first study, the trade-off triggered upon pathogen attack was eliminated by simultaneously enhancing the jasmonate-dependent defense response and reducing the activity of the phytochrome B (phyB)-dependent growth suppression pathway. These plants maintained their robust growth and defense capability against herbivorous insects⁷. In a second study, the stimulation of a specific branch of brassinosteroid signaling resulted in increased tolerance to drought stress without loss of growth⁸. However, phyB and brassinosteroids regulate multiple aspects of plant physiology. Indeed, loss of phyB activity also resulted in reduced photosynthetic capacity, but the decrease in energy supply was compensated by a reduction in leaf thickness, and brassinosteroids are also known to stimulate plant growth, so a more precise method of uncoupling growth inhibition from defense responses would be required. Moreover, even if the trade-off is not caused by competition for resources, a pivotal question remains unanswered: does the genetically-driven redistribution of resources confer an advantage under stress conditions, or is there an alternative benefit to the observed trade-off? To address this question, we have targeted the DELLA pathway to generate plants that specifically overcome the mechanism of growth inhibition by stress and studied their performance under water limitation. Studies in Arabidopsis thaliana have shown that DELLAs play an important role in limiting growth under stress^9,10. By eliminating DELLA activity, inflorescence growth can occur even under stress conditions. However, DELLA proteins also promote oxidative...