Optimisation of a somatic embryogenesis and transformation protocol for farmer-preferred cassava cultivars in Kenya

Cassava ( Manihot esculenta Crantz ) is a major food crop in developing countries, and holds potential for industrial use. It is, however, affected by various biotic and abiotic stresses that greatly affect its production. The existing regeneration and transformation protocols are not compatible with all cassava cultivars, thus efficient and robust transformation and regeneration protocols for farmer-preferred cultivars need to be optimised for ease of transfer of novel genes. The objective of this study was to develop an efficient transformation and regeneration protocol for a farmer-preferred Kenyan cassava cultivar. We cultured immature leaf lobe and stem explants on Murashige and Skoog (MS) medium, supplemented with varying concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), Picloram and \ue1-naphthalene acetic acid (NAA). Plants were recovered on media with 6-Benzylaminopurine (BAP) and GA3 under a 16 hour light/8 hour darkness photoperiod regime. Results showed high regeneration and transformation frequencies for both cultivars. High frequencies of callus induction (>98%) for both cultivars, were obtained when 2,4-D and Picloram were used. Similarly, both auxins initiated somatic embryogenesis, with Picloram producing the highest frequency of somatic embryos (>92%) in TMS 60444, using stem explants. Gus assays revealed high frequencies of transformation of >77% (TMS 60444) and 60% (Kibanda meno mkubwa). This protocol offers promising perspectives for rapid improvement of these cultivars and, therefore, provides a platform for cleaning planting materials, as well as cassava genetic improvement programmes such as control of viral diseases.Le manioc ( Manihot esculenta Crantz ) est une culture vivri\ue8re de grande importance pour les pays en d\ue9veloppement, avec un potentiel pour l\u2019usage industriel. N\ue9anmoins, le manioc est sujet \ue0 des stress d\u2019origines biotique et abiotique, affectant sa production. Les protocoles de r\ue9g\ue9n\ue9ration et de transformation existante ne sont pas compatibles avec toutes les accessions de manioc. Ainsi, il est n\ue9cessaire de d\ue9velopper des protocoles de r\ue9g\ue9n\ue9ration et de transformation efficaces pour les accessions adopt\ue9es par les paysans, afin de faciliter les transferts de g\ue8nes d\u2019int\ue9r\ueat. L\u2019objectif de cet etude \ue9tait de d\ue9velopper un protocole de r\ue9g\ue9n\ue9ration et de transformation adapte a la vari\ue9t\ue9 de manioc. Des feuilles et tiges immatures ont \ue9t\ue9 cultiv\ue9es sur des media Murashige et Skoog (MS), auxquels diff\ue9rentes concentrations de 2,4-dichlorophenoxyacetic acide (2,4-D), Picloram et \ue1-naphtal\ue8ne ac\ue9tique acide (NAA). Les plantes ont \ue9t\ue9 recouvertes de 6-Benzylaminopurine (BAP) et GA3 sous une photop\ue9riode de 16h jour/8h nuit. Les r\ue9sultats ont montr\ue9 des fr\ue9quences \ue9lev\ue9es de r\ue9g\ue9n\ue9ration et de transformation pour les deux cultivars Kibanda meno mkubwa et TMS 60444. Des fr\ue9quences \ue9lev\ue9es d\u2019induction de callosit\ue9s (>98%) ont \ue9t\ue9 obtenues pour les deux cultivars, lorsque 2,4-D et Picloram ont \ue9t\ue9 utilis\ue9s. De la m\ueame fa\ue7on, les deux embryogen\ue8ses somatiques initi\ue9es a l\u2019auxine, avec des explants de tiges et du Picloram ont exhibe la fr\ue9quence la plus \ue9lev\ue9e d\u2019embryon somatique (>92%) en TMS 60444. Des essais de Gus ont r\ue9v\ue9l\ue9s des fr\ue9quences \ue9lev\ue9es de transformation >77% (TMS 60444) et 60% (Kibanda meno mkubwa). Ce protocole offre des perspectives pour l\u2019am\ue9lioration rapide de ces cultivars, et par cons\ue9quent, fournit une plateforme pour la production de mat\ue9riels de culture propres, mais aussi servira d\u2019outil dans les programmes d\u2019am\ue9lioration g\ue9n\ue9tique visant la lutte contre les maladies virales

Integrated global assessment of the natural forest carbon potential

Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system1. Remote-sensing estimates to quantify carbon losses from global forests2,3,4,5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced6 and satellite-derived approaches2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets

The global distribution and drivers of wood density and their impact on forest carbon stocks.

The density of wood is a key indicator of the carbon investment strategies of trees, impacting productivity and carbon storage. Despite its importance, the global variation in wood density and its environmental controls remain poorly understood, preventing accurate predictions of global forest carbon stocks. Here we analyse information from 1.1 million forest inventory plots alongside wood density data from 10,703 tree species to create a spatially explicit understanding of the global wood density distribution and its drivers. Our findings reveal a pronounced latitudinal gradient, with wood in tropical forests being up to 30% denser than that in boreal forests. In both angiosperms and gymnosperms, hydrothermal conditions represented by annual mean temperature and soil moisture emerged as the primary factors influencing the variation in wood density globally. This indicates similar environmental filters and evolutionary adaptations among distinct plant groups, underscoring the essential role of abiotic factors in determining wood density in forest ecosystems. Additionally, our study highlights the prominent role of disturbance, such as human modification and fire risk, in influencing wood density at more local scales. Factoring in the spatial variation of wood density notably changes the estimates of forest carbon stocks, leading to differences of up to 21% within biomes. Therefore, our research contributes to a deeper understanding of terrestrial biomass distribution and how environmental changes and disturbances impact forest ecosystems

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers

HIV-1-specific mucosal IgA in a cohort of HIV-1-resistant Kenyan sex workers

Objectives: Most HIV-1 transmission is sexual; therefore, immune responses in the genital mucosa may be important in mediating protection against HIV infection. This study examined HIV-1-specific mucosal IgA in a cohort of HIV-1-resistant Kenyan female sex workers. Methods: HIV-1-specific immune responses were compared in HIV-1-resistant and HIV-1-infected sex workers, and in lower risk uninfected women. Cervical and vaginal samples from each group were tested for HIV-1-specific IgA and IgG by enzyme immunoassay. Systemic T-helper lymphocyte cell responses to HIV-1 envelope peptide epitopes were assayed using an interleukin 2 bioassay. HIV-1 risk-taking behaviours were assessed using standardized questionnaires. Results: HIV-1-specific IgA was present in the genital tract of 16 out of 21 (76%) HIV-1-resistant sex workers, five out of 19 (26%) infected women, and three out of 28 (11%) lower risk women (P < 0.0001). Among lower risk women, the presence of HIV-1-specific IgA was associated with HIV-1 risk-taking behaviour. Systemic T-helper lymphocyte responses to HIV-1 envelope peptides were present in 11 out of 20 (55%) HIV-1-resistant women, four out of 18 (22%) infected women, and one out of 25 (4%) lower risk women (P < 0.001). T-helper lymphocyte responses did not correlate with the presence or titre of virus-specific mucosal IgA in any study group. Conclusions: HIV-1-specific IgA is present in the genital tract of most HIV-1-resistant Kenyan sex workers, and of a minority of lower risk uninfected women, where it is associated with risk-taking behaviour. These data suggest a role for mucosal HIV-1-specific IgA responses in HIV-1 resistance, independent of host cellular responses