Gibberellins negatively regulate the development of Medicago truncatula root system

Camille Fonouni-Farde,Florian Frugier,Anouck Diet,Abdelhafid Bendahmane,Carole Laffont,Halima Morin,Ambre Miassod

doi:10.1038/s41598-019-38876-1

Camille Fonouni-Farde, Florian Frugier + Show 5 more

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The root system displays a remarkable plasticity that enables plants to adapt to changing environmental conditions. This plasticity is tightly linked to the activity of root apical meristems (RAMs) and to the formation of lateral roots, both controlled by related hormonal crosstalks. In Arabidopsis thaliana, gibberellins (GAs) were shown to positively control RAM growth and the formation of lateral roots. However, we showed in Medicago truncatula that GAs negatively regulate root growth and RAM size as well as the number of lateral roots depending at least on the MtDELLA1 protein. By using confocal microscopy and molecular analyses, we showed that GAs primarily regulate RAM size by affecting cortical cell expansion and additionally negatively regulate a subset of cytokinin-induced root expansin encoding genes. Moreover, GAs reduce the number of cortical cell layers, resulting in the formation of both shorter and thinner roots. These results suggest contrasting effects of GA regulations on the root system architecture depending on plant species.

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Roots exhibit a remarkable developmental plasticity representing a key adaptive trait that enables plant adaptation to external conditions
To investigate the role of GAs in M. truncatula root development, we first characterized the effect of exogenous applications of bioactive GA3 and of the GA-biosynthesis inhibitor paclobutrazol (PAC) on the primary root growth of wild-type (WT) plants, two weeks post-germination (Fig. 1A,B)
As DELLA proteins are critical regulators of GA-dependent responses[13], and as previous studies conducted in M. truncatula reported that the three MtDELLA genes identified in the genome are expressed in the RAM30–32, we hypothesized that GAs could regulate primary root growth depending on DELLA proteins

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Roots exhibit a remarkable developmental plasticity representing a key adaptive trait that enables plant adaptation to external conditions. It was proposed that high amounts of GAs in the A. thaliana TZ of the RAM induce the degradation of the DELLA protein RGA, resulting in the inactivation and decrease of the expression of the CK signaling transcription factor ARR1. This decrease, leading to the inhibition of the regulation of cell differentiation by CKs, promotes auxin-dependent cell divisions[9,10,12]. GAs negatively regulate the number of cortical cell layers initiated in the apical part of the RAM, and impact on the global root diameter

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