Soybean (Ibc3), Parasponia, and Trema hemoglobin gene promoters retain symbiotic and nonsymbiotic specificity in transgenic Casuarinaceae : implications for hemoglobin gene evolution and root nodule symbioses

The purpose of this study was to compare the control of expression of legume and nonlegume hemoglobin genes. We used the #Casuarina glauca and #Allocasuarina verticillata transformation system to examine the properties of the soybean (Ibc3), #Parasponia andersonii, and #Trema tomentosa hemoglobin gene promoters in actinorhizal plants. Expression of the hemoglobin promoters gus genes was examined by fluorometric and histochemical assays. The fluorometric assays in various organs showed that the soybean and #P. andersonii promoters were most active in nodules whereas the #T. tomentosa promoter gave a very high activity in roots. The histochemical study showed that GUS activity directed by the soybean and the #P. andersonii gus chimeric genes appeared mainly confined to the infected cells of the #C. glauca and #A. verticillata nodules. The #T. tomentosa hemoglobin promoter was primarily expressed in the root's cortex and vascular tissue. The results indicate that the soybean, #P. andersonii, and #T. tomentosa hemoglobin promoters retain their cell-specific expression in transgenic members of the #Casuarinaceae, suggesting a close relationship between legume, #Ulmaceae member, and actinorhizal hemoglobin genes. The conservation of the mechanism for nodule-specific expression of soybean, #P. andersonii, and #C. glauca and #A. verticillata$ hemoglobin genes is discussed in view of recent molecular phylogenetic data that suggest a single origin for the pre-disposition to form root nodule symbioses. (Résumé d'auteur

Evaluation de la contamination par les éléments-traces métalliques dans une zone minière du Maroc oriental = Assessment of contamination by metallic trace elements in a mining area of eastern Morocco

La contamination des sols et des résidus miniers dans la région orientale du Maroc a été évaluée par dosage des éléments-traces métalliques (ETM) (As, Cd, Cu, Ni, Pb et Zn) par ICP-AES (inductively coupled plasma-atomic emission spectrometry). Ce travail révèle une contamination importante des sites étudiés et souligne une grande variabilité dans les concentrations en ETM en fonction de l_élément analysé et du site étudié. L'index de pollution des stations étudiées est généralement trés élevé du fait de la présence simultaneée de plusieurs de ces éléments. Cette combinaison de différents ETM rend les sols de la région toxiques pour la flore, la faune et les populations locales. Une analyse des espèces végétales qui se développent sur ces zones polluées est envisagée dans le cadre de la mise en place d'un programme de phytoremédiatio

The Casuarina NIN gene is transcriptionally activated throughout Frankia root infection as well as in response to bacterial diffusible signals

Root nodule symbioses (RNS) allow plants to acquire atmospheric nitrogen by establishing an intimate relationship with either rhizobia, the symbionts of legumes or Frankia in the case of actinorhizal plants. In legumes, NIN (Nodule INception) genes encode key transcription factors involved in nodulation. Here we report the characterization of CgNIN, a NIN gene from the actinorhizal tree Casuarina glauca using both phylogenetic analysis and transgenic plants expressing either ProCgNIN::reporter gene fusions or CgNIN RNAi constructs. We have found that CgNIN belongs to the same phylogenetic group as other symbiotic NIN genes and CgNIN is able to complement a legume nin mutant for the early steps of nodule development. CgNIN expression is correlated with infection by Frankia, including preinfection stages in developing root hairs, and is induced by culture supernatants. Knockdown mutants were impaired for nodulation and early root hair deformation responses were severely affected. However, no mycorrhizal phenotype was observed and no induction of CgNIN expression was detected in mycorrhizas. Our results indicate that elements specifically required for nodulation include NIN and possibly related gene networks derived from the nitrate signalling pathways

Broad-spectrum resistance to bacterial blight in rice using genome editing

Bacterial blight of rice is an important disease in Asia and Africa. The pathogen, Xanthomonas oryzae pv. oryzae (Xoo), secretes one or more of six known transcription-activator-like effectors (TALes) that bind specific promoter sequences and induce, at minimum, one of the three host sucrose transporter genes SWEET11, SWEET13 and SWEET14, the expression of which is required for disease susceptibility. We used CRISPR-Cas9-mediated genome editing to introduce mutations in all three SWEET gene promoters. Editing was further informed by sequence analyses of TALe genes in 63 Xoo strains, which revealed multiple TALe variants for SWEET13 alleles. Mutations were also created in SWEET14, which is also targeted by two TALes from an African Xoo lineage. A total of five promoter mutations were simultaneously introduced into the rice line Kitaake and the elite mega varieties IR64 and Ciherang-Sub1. Paddy trials showed that genome-edited SWEET promoters endow rice lines with robust, broad-spectrum resistance

Broad-spectrum resistance to bacterial blight in rice using genome editing

Bacterial blight of rice is an important disease in Asia and Africa. The pathogen, Xanthomonas oryzae pv. oryzae (Xoo), secretes one or more of six known transcription-activator-like effectors (TALes) that bind specific promoter sequences and induce, at minimum, one of the three host sucrose transporter genes SWEET11, SWEET13 and SWEET14, the expression of which is required for disease susceptibility. We used CRISPR-Cas9-mediated genome editing to introduce mutations in all three SWEET gene promoters. Editing was further informed by sequence analyses of TALe genes in 63 Xoo strains, which revealed multiple TALe variants for SWEET13 alleles. Mutations were also created in SWEET14, which is also targeted by two TALes from an African Xoo lineage. A total of five promoter mutations were simultaneously introduced into the rice line Kitaake and the elite mega varieties IR64 and Ciherang-Sub1. Paddy trials showed that genome-edited SWEET promoters endow rice lines with robust, broad-spectrum resistance

Molecular Methods for Research on Actinorhiza

Actinorhizal root nodules result from the interaction between a nitrogen-fixing actinomycete from the genus Frankia and roots of dicotyledonous trees and shrubs belonging to 25 genera within 8 plant families. Most actinorhizal plants can reach high rates of nitrogen fixation comparable to those found in root nodule symbiosis of the legumes. As a consequence, these trees are able to grow in poor and disturbed soils and are important elements in plant communities worldwide. While the basic knowledge of these symbiotic associations is still poorly understood, actinorhizal symbioses emerged recently as original systems to explore developmental strategies to form nitrogen-fixing nodules. Many tools have been developed in recent years to explore the interaction between Frankia and actinorhizal plants including molecular biology, biochemistry, and genomics. However, technical difficulties are often encountered to explore these symbiotic interactions, mainly linked to the woody nature of the plant species and to the lack of genetic tools for their bacterial symbionts. In this chapter, we report an inventory of the main recent molecular tools and techniques developed for studying actinorhizae