Genetic transformation of forest trees

In this review, the recent progress on genetic transformation of forest trees were discussed. Its described also, different applications of genetic engineering for improving forest trees or understanding the mechanisms governing genes expression in woody plants. Key words: Genetic transformation, transgenic forest trees, gene expression. African Journal of Biotechnology Vol.2(10) 2003: 328-33

Le s symbioses fixatrices d’azote : types et régulateurs t ranscriptionnels de la nodulation

Les symbioses fixatrices d’azote sont des interactions à bénéfice réciproque entre certaines espèces végétales (légumineuses et plantes actinorhiziennes principalement) et des microorganismes du sol ( r hizobium ou Frankia ). Ces symbioses contribuent de façon considérable à la nutrition azotée de ces plantes e t donc à leur développement particulièrement sur l es sols pauvres en azote . L’établissement de ces symbioses démarre par un dialogue moléculaire , puis par la formation de structures appelées nodules ou nodosités , siège des échanges entre les deux partenaires (plante et bactérie) La formation et le développement de nodules requièrent la médiation de gènes spécifiques parmi les quels figurent les régulateurs transcriptionnels ( facteurs de transcription et microARN) microARN). Des facteurs de transcription dont CYCLOPS, NSP1 et NSP2 communs entre les symbioses r hizobium légumineuse et Frankia plante actinorhizienne ont été caractérisés à d ifférents stades du développement du nodule Ils interagissent avec les protéines DE LLA pour induire l’expression du gène NIN , n écessaire à l’initiation de l’infection . Ces facteurs de transcription sont régulés par divers microARN. Cette revue résume l es types de symbioses fixatrices d’azote et les récentes avancées sur l es régulateurs transcriptionnels impliqué s dans l es étapes de pré infection, d’infection et d’organogenèse du nodule . Pour ce faire, nous avons collecté et analysé des données pertinentes de la littérature sur des études moléculaires et cellulaires des symbioses fixatrices d’azote

The emerging oilseed crop Sesamum indicum enters the “Omics” era

Sesame (Sesamum indicum L.) is one of the oldest oilseed crops widely grown in Africa and Asia for its high-quality nutritional seeds. It is well adapted to harsh environments and constitutes an alternative cash crop for smallholders in developing countries. Despite its economic and nutritional importance, sesame is considered as an orphan crop because it has received very little attention from science. As a consequence, it lags behind the other major oil crops as far as genetic improvement is concerned. In recent years, the scenario has considerably changed with the decoding of the sesame nuclear genome leading to the development of various genomic resources including molecular markers, comprehensive genetic maps, high-quality transcriptome assemblies, web-based functional databases and diverse daft genome sequences. The availability of these tools in association with the discovery of candidate genes and quantitative trait locis for key agronomic traits including high oil content and quality, waterlogging and drought tolerance, disease resistance, cytoplasmic male sterility, high yield, pave the way to the development of some new strategies for sesame genetic improvement. As a result, sesame has graduated from an “orphan crop” to a “genomic resource-rich crop.” With the limited research teams working on sesame worldwide, more synergic efforts are needed to integrate these resources in sesame breeding for productivity upsurge, ensuring food security and improved livelihood in developing countries. This review retraces the evolution of sesame research by highlighting the recent advances in the “Omics” area and also critically discusses the future prospects for a further genetic improvement and a better expansion of this crop. (Résumé d'auteur

Insight into the AP2/ERF transcription factor superfamily in sesame and expression profiling of DREB subfamily under drought stress

Background. Sesame is an important oilseed crop mainly grown in inclement areas with high temperatures and frequent drought. Thus, drought constitutes one of the major constraints of its production. The AP2/ERF is a large family of transcription factors known to play significant roles in various plant processes including biotic and abiotic stress responses. Despite their importance, little is known about sesame AP2/ERF genes. This constitutes a limitation for drought-tolerance candidate genes discovery and breeding for tolerance to water deficit. Results. One hundred thirty-two AP2/ERF genes were identified in the sesame genome. Based on the number of domains, conserved motifs, genes structure and phylogenetic analysis including 5 relatives species, they were classified into 24 AP2, 41 DREB, 61 ERF, 4 RAV and 2 Soloist. The number of sesame AP2/ERF genes was relatively few compared to that of other relatives, probably due to gene loss in ERF and DREB subfamilies during evolutionary process. In general, the AP2/ERF genes were expressed differently in different tissues but exhibited the highest expression levels in the root. Mostly all DREB genes were responsive to drought stress. Regulation by drought is not specific to one DREB group but depends on the genes and the group A6 and A1 appeared to be more actively expressed to cope with drought. Conclusions. This study provides insights into the classification, evolution and basic functional analysis of AP2/ERF genes in sesame which revealed their putative involvement in multiple tissue-/developmental stages. Out of 20 genes which were significantly up- /down-regulated under drought stress, the gene AP2si16 may be considered as potential candidate gene for further functional validation as well for utilization in sesame improvement programs for drought stress tolerance. (Résumé d'auteur

Screening cowpea [Vigna unguiculata (L.) Walp.] varieties by inducing water deficit and RAPD analyses

The effects of water deficit induced by polyethylene glycol-6000 on some cowpea varieties, which belong to the national germplasm in Senegal are reported. Our results showed that, the length of the epicotyl was not affected by water deficit but the length of primary root was influenced only in Mouride variety. Water deficit influenced mostly the number of lateral roots. The 985 variety showed a great increase of its lateral root numbers and could be considered a drought tolerant variety. In contrast, the IT81D-1137 variety is very sensitive to water deficit because its lateral root number were reduced 3.8 fold compared to the control. These physiological studies were complemented by analyzing the genetic diversity of these varieties with random amplified polymorphic DNA (RAPD). The RAPD analysis suggested that the samples were also genetically diverse. Key Words: Vigna unguiculata, drought tolerance, PEG, RAPD. African Journal of Biotechnology Vol.3(3) 2004: 174-17

Transcriptomic, biochemical and physio-anatomical investigations shed more light on responses to drought stress in two contrasting sesame genotypes

Sesame is an important oilseed crop with a high oil quality. It is prone to drought stress in the arid and semi-arid areas where it is widely grown. This study aims to decipher the response of tolerant (DT) and sensitive (DS) genotypes to progressive drought based on transcriptome, biochemical and physio-anatomical characterizations. Results indicated that under severe stress, DT relied on a well-functioning taproot while DS displayed a disintegrated root due to collapsed cortical cells. This was attributed to a higher accumulation of osmoprotectants and strong activity of antioxidant enzymes especially peroxidases in DT. From roots, DT could supply water to the aboveground tissues to ensure photosynthetic activities and improve endurance under stress. Temporal transcriptome sequencing under drought further confirmed that DT strongly activated genes related to antioxidant activity, osmoprotection and hormonal signaling pathways including abscisic acid and Ethylene. Furthermore, DT displayed unique differentially expressed genes in root functioning as peroxidases, interleukin receptor-associated kinase, heat shock proteins, APETALA2/ethylene-responsive element-binding protein and mitogen activated protein kinase, to effectively scavenge reactive oxygen species and preserve root cell integrity. Finally, 61 candidate genes conferring higher drought tolerance in DT were discovered and may constitute useful resources for drought tolerance improvement in sesame. (Résumé d'auteur

The genetic basis of drought tolerance in the high oil crop Sesamum indicum

Unlike most of the important food crops, sesame can survive drought but severe and repeated drought episodes, especially occurring during the reproductive stage, significantly curtail the productivity of this high oil crop. Genome‐wide association study was conducted for traits related to drought tolerance using 400 diverse sesame accessions, including landraces and modern cultivars. Ten stable QTLs explaining more than 40% of the phenotypic variation and located on four linkage groups were significantly associated with drought tolerance related traits. Accessions from the tropical area harboured higher numbers of drought tolerance alleles at the peak loci and were found to be more tolerant than those from the northern area, indicating a long‐term genetic adaptation to drought‐prone environments. We found that sesame has already fixed important alleles conferring survival to drought which may explain its relative high drought tolerance. However, most of the alleles crucial for productivity and yield maintenance under drought conditions are far from been fixed. This study also revealed that pyramiding the favourable alleles observed at the peak loci is of high potential for enhancing drought tolerance in sesame. In addition, our results highlighted two important pleiotropic QTLs harbouring known and unreported drought tolerance genes such as SiABI4, SiTTM3, SiGOLS1, SiNIMIN1 and SiSAM. By integrating candidate gene association study, gene expression and transgenic experiments, we demonstrated that SiSAM confers drought tolerance by modulating polyamine levels and ROS homeostasis, and a missense mutation in the coding region partly contributes to the natural variation of drought tolerance in sesame

Agro-physiological responses of 10 west Africa sorghum varieties to early water deficit assessed by UAV and ground phenotyping

Sorghum is a staple food for many in the Sahel. However, it often faces earlystage water deficit resulting in production decrease. Research is focusing on developing early drought tolerant varieties. This study assessed the effects of early drought stress on 10 elite varieties of West African sorghum collection tested over 2 years (2018-2019) in Bambey (Senegal). Water stress was applied by withholding irrigation 25 days after sowing for one month, followed by optimal irrigation until maturity. Soil moisture and agro-physiomorphological traits were monitored. Results showed highly significant effects of early drought stress on sorghum plants growth. The combined analysis of variance revealed highly significant differences (P ≤ 0.01) between varieties in the different environments for most traits studied. Under water deficit, the genotypic adaptation was linked to the capacity of varieties to increase the dead leaves weight and the roots length density and to reduce photosynthesis rate, stomata conductance, and leaf transpiration. The analysis of spectral indices across water treatments revealed significant variation. However, the differential responses between varieties remained the same. Fadda (V1), Nieleni (V2), Soumba (V8) and 621B (V9) showed promising behavior under drought stress and could be suitable for further use in West Africa

Genetic diversity in cowpea [Vigna unguiculata (L.) Walp.] varieties determined by ARA and RAPD techniques

Cowpea, Vigna unguiculata (L.) Walp. presents phenotypical variabilities and in order to study the genetic diversity of cultivated Senegalese varieties, two experimental approaches were used. First, a physiological characterization based on nitrogen fixation was used to assess cowpea breeding lines. Inoculation with two Bradyrhizobium strains (NGR234 and ISRA312), showed a difference in nitrogen fixation potential between the cowpea varieties. Diongoma is the highest nitrogen fixing variety, whereas Mouride is the lowest. The second approach employed genetic characterization based on DNA polymorphism to screen. Results suggest that random amplified polymorphic DNA (RAPD) technology can be used to reorganize the national germplasm in order to eliminate the putative duplicates, and to identify elite varieties. (African Journal of Biotechnology: 2003 2(2): 48-50

The genetic basis of phenotypic plasticity in sorghum: Dissection with an environmental profiling

Identifying the environmental and genetic drivers that occur in phenotype's expression can help to dissect complex traits. This study aims to identify the critical sorghum growth period sensitive to environmental stimuli and to assess genetic loci's effects along the environmental gradient. We evaluated a mapping population of 253 recombinant inbred lines (RIL) in five natural environments focusing on two photoperiod sensitivity traits: flag leaf ligulation and plant height as proxies for assessing grain mold resistance. Grain mold severity scores have been rated and yield components (panicle and grain weight per plant) have been measured. From initial results, variance component analysis attributed 21.50% of the flag leaf ligulation to the environment, and 41.22% of the variation to the genotype. For the plant height, environmental effects accounted for 51.16 % of the phenotypic variance, followed by the genotype effect (24.96%). Using environmental means, we applied the joint regression analysis to unravel the pattern underneath the trait variation. Further, we will implement the CERIS (Critical Environmental Regressor through Informed Search) framework to replace environmental means with an environmental index biologically informing. The combination of environmental parameters: photoperiod (daylength), growing degree day (GDD, °C), diurnal temperature range (DTR, °C), photothermal time (PTT, °C), precipitation (PR, mm); and growth windows with the strongest correlation will be chosen as the environmental index. By regressing again the phenotypes of each RIL on the environment index, two reaction-norm parameters (intercept and slope) will be obtained. The genetic map will then be built using reaction-norm values (as phenotypes) with 952 SNP markers from 3495 SNPs generated by DArTag technology, to identify the genetic loci underlying phenotypic plasticity along environment gradient