RESUMEN
Compartmentation of photosynthetic reactions between mesophyll and bundle sheath cells is a key feature of C4 photosynthesis and depends on the cell-specific accumulation of major C4 enzymes, such as phosphoenolpyruvate carboxylase 1. The ZmPEPC1 upstream region, which drives light-inducible and mesophyll-specific gene expression in maize, has been shown to keep the same properties when introduced into rice (C3 plant), indicating that rice has the transcription factors (TFs) needed to confer C4 -like gene expression. Using a yeast one-hybrid approach, we identified OsbHLH112, a rice basic Helix-Loop-Helix (bHLH) TF that interacts with the maize ZmPEPC1 upstream region. Moreover, we found that maize OsbHLH112 homologues, ZmbHLH80, and ZmbHLH90, also interact with the ZmPEPC1 upstream region, suggesting that these C4 regulators were co-opted from C3 plants. A transactivation assay in maize mesophyll protoplasts revealed that ZmbHLH80 represses, whereas ZmbHLH90 activates, ZmPEPC1 expression. In addition, ZmbHLH80 was shown to impair the ZmPEPC1 promoter activation caused by ZmbHLH90. We showed that ZmbHLH80 and ZmbHLH90 bind to the same cis-element within the ZmPEPC1 upstream region either as homodimers or heterodimers. The formation of homo- and heterodimers with higher oligomeric forms promoted by ZmbHLH80 may explain its negative effect on gene transcription. Gene expression analysis revealed that ZmbHLH80 is preferentially expressed in bundle sheath cells, whereas ZmbHLH90 does not show a clear cell-specific expression pattern. Altogether, our results led us to propose a model in which ZmbHLH80 contributes to mesophyll-specific ZmPEPC1 gene expression by impairing ZmbHLH90-mediated ZmPEPC1 activation in the bundle sheath cells.
Asunto(s)
Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/fisiología , Proteínas de Plantas/fisiología , Zea mays/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Regulación de la Expresión Génica de las Plantas , Técnicas de Sonda Molecular , Oryza/genética , Fotosíntesis/genética , Proteínas de Plantas/genética , Regiones Promotoras Genéticas , Zea mays/metabolismoRESUMEN
Knowledge of the levels and distribution of genetic diversity is important for designing conservation strategies for threatened and endangered species so as to guarantee sustainable survival of populations and to preserve their evolutionary potential. Picconia azorica is a valuable Azorean endemic species recently classified as endangered. To contribute with information useful for the establishment of conservation programmes, the genetic variability and differentiation among 230 samples from 11 populations collected in three Azorean islands was accessed with eight inter-simple sequence repeat markers. A total of 64 polymorphic loci were detected. The majority of genetic variability was found within populations and no genetic structure was detected between populations and between islands. Also the coefficient of genetic differentiation and the level of gene flow indicate that geographical distances do not act as barriers for gene flow. In order to ensure the survival of populations in situ and ex situ management practices should be considered, including artificial propagation through the use of plant tissue culture techniques, not only for the restoration of habitat but also for the sustainable use of its valuable wood.