Overexpression of MADS-box Gene AGAMOUS-LIKE 12 Activates Root Development in Juglans sp. and Arabidopsis thaliana

Until recently, the roles of plant MADS-box genes have mainly been characterized during inflorescence and flower differentiation. In order to precise the roles of AGAMOUS-LIKE 12, one of the few MADS-box genes preferentially expressed in roots, we placed its cDNA under the control of the double 35S CaMV promoter to produce transgenic walnut tree and Arabidopsis plants. In Juglans sp., transgenic somatic embryos showed significantly higher germination rates but abnormal development of their shoot apex prevented their conversion into plants. In addition, a wide range of developmental abnormalities corresponding to ectopic root-like structures affected the transgenic lines suggesting partial reorientations of the embryonic program toward root differentiation. In Arabidopsis, AtAGL12 overexpression lead to the production of faster growing plants presenting dramatically wider and shorter root phenotypes linked to increased meristematic cell numbers within the root apex. In the upper part of the roots, abnormal cell divisions patterns within the pericycle layer generated large ectopic cell masses that did not prevent plants to grow. Taken together, our results confirm in both species that AGL12 positively regulates root meristem cell division and promotes overall root vascular tissue formation. Genetic engineering of AGL12 expression levels could be useful to modulate root architecture and development

Etude fonctionnelle des facteurs de transcription AGL12 et CrMYC2 dans les processus de différenciation morphologique et de différenciation métabolique de racines et de cellules végétales cultivées in vitro

Ce travail de thèse a consisté à étudier les rôles joués par les facteurs de transcription AGL12 et CrMYC2 dans les processus de différenciation morphologique et/ou métabolique au niveau d'embryons somatiques de noyer et de suspensions cellulaires de Catharanthus roseus.L'expression du gène Agl12 d'Arabidospis thaliana stimule le développement des racines des embryons somatiques de noyer. Les cellules de C. roseus exprimant Agl12 permet s'organisent en pseudo-tissu et synthétisent de l'ajmalicine. Ces résultats assignent un rôle important à AGL12 lors de la différenciation racinaire.CrMYC2 est capable d'interagir avec la G-box du promoteur du gène Str, et est rapidement et transitoirement induit dans des cellules de C. roseus en réponse à un eliciteur fongique et au méthyl jasmonate. La sur-expression de CrMYC2 dans les suspensions cellulaires n'a pas d'effet sur la régulation de l'expression du gène Str, mais semble avoir un effet inhibiteur sur l'expression des gènes Dxs et Chs.The goal of this work was to characterize the roles of two transcription factors (AGL12 and CrMYC2) during the morphological and metabolic differentiation occuring in walnut somatic embryos and Catharanthus roseus cell suspensions.Overexpression of the Agl12 gene from Arabidopsis thaliana enhances the rooting abilities of walnut somatic embryos. C. roseus transgenic cells expressing this gene are grouped in globular body and biosynthetize ajmalicine. Taken together, these results suggest that AGL12 plays an important role in root differentiation processes.The CrMYC2 transcription factor, which interact with the G-box localized within the Str gene promoter, is rapidly and transiently induced in C. roseus cells in response to a treatment with a fungal elicitor or methyl jasmonate. The expression of CrMYC2 in transgenic cells has no significant impact on the regulation of the Str gene expression but seems to have an inhibitory effect on the expression of the Dxs and Chs.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF

Transcription Factor Networks. Pathways to the Knowledge of Root Development

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Haustorium Inducing Factors for Parasitic Orobanchaceae

International audienceParasitic plants in the Orobanchaceae family include devastating weed species, such as Striga, Orobanche, and Phelipanche, which infest important crops and cause economic losses of over a billion US dollars worldwide, yet the molecular and cellular processes responsible for such parasitic relationships remain largely unknown. Parasitic species of the Orobanchaceae family form specialized invasion organs called haustoria on their roots to enable the invasion of host root tissues. The process of forming haustoria can be divided into two steps, prehaustorium formation and haustorium maturation, the processes occurring before and after host attachment, respectively. Prehaustorium formation is provoked by host-derived signal molecules, collectively called haustorium-inducing factors (HIFs). Cell wall-related quinones and phenolics have been known for a long time to induce haustoria in many Orobanchaceae species. Although such phenolics are widely produced in plants, structural specificities exist among these molecules that modulate their competency to induce haustoria in different parasitic plant species. In addition, the plant hormone cytokinins, structurally distinct from phenolic compounds, also trigger prehaustorium formation in Orobanchaceae. Recent findings demonstrate their involvement as rhizopsheric HIFs for Orobanche and Phelipanche species and thus address new activities for cytokinins in haustorium formation in Orobanchaceae, as well as in rhizospheric signaling. This review highlights haustorium-inducing signals in the Orobanchaceae family in the context of their host origin, action mechanisms, and species specificity

CrMYC1, a Catharanthus roseus elicitor- and jasmonate-responsive bHLH transcription factor that binds the G-box element of the strictosidine synthase gene promoter.

A cDNA encoding a bHLH transcription factor was isolated by the yeast one-hybrid system from a Catharanthus roseus cDNA library using the G-box element of the Strictosidine synthase gene promoter as bait. The corresponding protein (named CrMYC1) was shown to bind specifically to the G-box in yeast. In C. roseus suspension cells CrMYC1 mRNA levels are induced by fungal elicitor and jasmonate suggesting that CrMYC1 may be involved in the regulation of gene expression in response to these signals.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Brassinosteroid signaling-dependent root responses to prolonged elevated ambient temperature

Due to their sessile nature, plants have to cope with and adjust to their fluctuating environment. Temperature elevation stimulates the growth of Arabidopsis aerial parts. This process is mediated by increased biosynthesis of the growth-promoting hormone auxin. How plant roots respond to elevated ambient temperature is however still elusive. Here we present strong evidence that temperature elevation impinges on brassinosteroid hormone signaling to alter root growth. We show that elevated temperature leads to increased root elongation, independently of auxin or factors known to drive temperature-mediated shoot growth. We further demonstrate that brassinosteroid signaling regulates root responses to elevated ambient temperature. Increased growth temperature specifically impacts on the level of the brassinosteroid receptor BRI1 to downregulate brassinosteroid signaling and mediate root elongation. Our results establish that BRI1 integrates temperature and brassinosteroid signaling to regulate root growth upon long-term changes in environmental conditions associated with global warming.Moderate heat stimulates the growth of Arabidopsis shoots in an auxin-dependent manner. Here, Martins et al. show that elevated ambient temperature modifies root growth by reducing the BRI1 brassinosteroid-receptor protein level and downregulating brassinosteroid signaling

Seed response to strigolactone is controlled by abscisic acid-independent DNA methylation in the obligate root parasitic plant, Phelipanche ramosa L. Pomel

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Haustorium initiation in the obligate parasitic plant Phelipanche ramosa involves a host-exudated cytokinin signal

The heterotrophic lifestyle of parasitic plants relies on the development of the haustorium, a specific infectious organ required for attachment to host roots. While haustorium development is initiated upon chemodetection of host-derived molecules in hemiparasitic plants, the induction of haustorium formation remains largely unknown in holoparasitic species such as Phelipanche ramosa. This work demonstrates that the root exudates of the host plant Brassica napus contain allelochemicals displaying haustorium-inducing activity on P. ramosa germinating seeds, which increases the parasite aggressiveness. A de novo assembled transcriptome and microarray approach with P. ramosa during early haustorium formation upon treatment with B. napus root exudates allowed the identification of differentially expressed genes involved in hormone signaling. Bioassays using exogenous cytokinins and the specific cytokinin receptor inhibitor PI-55 showed that cytokinins induced haustorium formation and increased parasite aggressiveness. Root exudates triggered the expression of cytokinin-responsive genes during early haustorium development in germinated seeds, and bio-guided UPLC-ESI(+)-/MS/MS analysis showed that these exudates contain a cytokinin with dihydrozeatin characteristics. These results suggest that cytokinins constitutively exudated from host roots play a major role in haustorium formation and aggressiveness in P. ramosa