Jasmonate Controls Leaf Growth by Repressing Cell Proliferation and the Onset of Endoreduplication while Maintaining a Potential Stand-By Mode    

Abstract

Phytohormones regulate plant growth from cell division to organ development. Jasmonates (JAs) are signaling molecules that have been implicated in stress-induced responses. However, they have also been shown to inhibit plant growth, but the mechanisms are not well understood. The effects of methyl jasmonate (MeJA) on leaf growth regulation were investigated in Arabidopsis (Arabidopsis thaliana) mutants altered in JA synthesis and perception, allene oxide synthase and coi1-16B (for coronatine insensitive1), respectively. We show that MeJA inhibits leaf growth through the JA receptor COI1 by reducing both cell number and size. Further investigations using flow cytometry analyses allowed us to evaluate ploidy levels and to monitor cell cycle progression in leaves and cotyledons of Arabidopsis and/or Nicotiana benthamiana at different stages of development. Additionally, a novel global transcription profiling analysis involving continuous treatment with MeJA was carried out to identify the molecular players whose expression is regulated during leaf development by this hormone and COI1. The results of these studies revealed that MeJA delays the switch from the mitotic cell cycle to the endoreduplication cycle, which accompanies cell expansion, in a COI1-dependent manner and inhibits the mitotic cycle itself, arresting cells in G1 phase prior to the S-phase transition. Significantly, we show that MeJA activates critical regulators of endoreduplication and affects the expression of key determinants of DNA replication. Our discoveries also suggest that MeJA may contribute to the maintenance of a cellular "stand-by mode" by keeping the expression of ribosomal genes at an elevated level. Finally, we propose a novel model for MeJA-regulated COI1-dependent leaf growth inhibition.

Wounding Triggers Callus Formation via Dynamic Hormonal and Transcriptional Changes

“…3). JA is known to block plant growth (Yan et al, 2007), and JA represses both cell proliferation and cell expansion to limit organ growth (Noir et al, 2013). Lack of JA's contribution in callus formation is therefore in line with previous studies, strongly suggesting that JA primarily mediates defense-related responses after wounding.…”

“…3B). To test whether this increase in JA level is required for callus formation, we performed a wound-induced callus-induction assay using aos (Park et al, 2002) and coronatine insensitive1-16B (coi1-16B: Noir et al, 2013), mutants defective in JA biosynthesis or signaling, respectively. As shown in Figure 3C, both mutants show slightly higher efficiency of callus formation compared to wild type, suggesting that JA synthesis and signaling are slightly inhibitory to callus formation at wound sites.…”

“…Cellular capacity of protein synthesis is tightly controlled according to the developmental and environmental conditions. Transcript level of ribosomal genes, for example, is higher in developing organs where cells actively proliferate than in maturing organs (Noir et al, 2013). Therefore, activation of genes encoding ribosomal proteins in cluster 3 may be associated with preparation for cell proliferation during callus formation, which is also observed before the onset of protoplast cell proliferation (Chupeau et al, 2013).…”

The effect of methyl jasmonate on selected physiological parameters of copper-treated Phaseolus coccineus plants

“…Next, it led to the reduction of cell growth (Schmidt et al 2010) and inhibited cell proliferation and elongation (Noir et al 2013). Additionally, MJ can directly or indirectly modulate the influence of auxin on root growth and development (Wasternack and Hause 2013).…”

“…and plant growth (Jubany-Marí et al 2010;Kobayashi et al 2010) and genes involved in photosynthesis, such as ribulose bisphosphate carboxylase/oxygenase (Rubisco), chlorophyll a/b-binding protein, light harvesting complex II, and early light-induced proteins, were down-regulated (Jung et al 2007). At a concentration of 50 lM or lower, MJ mostly, but not always (Noir et al 2013), stimulated plant growth, lateral root initiation and growth, dry matter accumulation, biomass production, photosynthetic pigment levels, and elevation of the net photosynthetic rate (Tung et al 1996;Mabood et al 2006;Piotrowska et al 2010;Wu et al 2012). However, the role of MJ in protecting plants from various abiotic stresses has been controversial.…”