RESUMO
GA biosynthesis and catabolism has been shown to play an important role in regulating tuberization in potato. Active GAs are inactivated in the stolon tips shortly after induction to tuberization. Overexpression of a GA inactivation gene results in an earlier tuberization phenotype, while reducing expression of the same gene results in delayed tuberization. In addition, overexpression of genes involved in GA biosynthesis results in delayed tuberization, while decreased expression of those genes results in earlied tuberization. The final step in GA biosynthesis is catalysed by StGA3ox1 and StGA3ox2 activity, that convert inactive forms of GA into active GA1 and GA4. In this study we cloned StGA3ox2 gene in an RNAi construct and used this construct to transform potato plants. The StGA3ox2 silenced plants were smaller and had shorter internodes. In addition, we assayed the concentrations of various GAs in the transgenic plants and showed an altered GA content. No difference was observed on the time point of tuber initiation. However, the transgenic clones had increased number of tubers with the same yield, resulting in smaller average tuber weight. In addition, we cloned the promoter of StGA3ox2 to direct expression of the GUS reporter gene to visualize the sites of GA biosynthesis in the potato plant. Finally, we discuss how changes of several GA levels can have an impact on shoot, stolon and tuber development, as well as the possible mechanisms that mediate feed-forward and feed-back regulation loops in the GA biosynthetic pathway in potato.
Assuntos
Giberelinas/metabolismo , Oxigenases de Função Mista/genética , Proteínas de Plantas/genética , Solanum tuberosum/crescimento & desenvolvimento , Solanum tuberosum/genética , Agrobacterium/genética , Vias Biossintéticas/efeitos dos fármacos , Clonagem Molecular , Regulação para Baixo/efeitos dos fármacos , Retroalimentação Fisiológica , Giberelinas/biossíntese , Oxigenases de Função Mista/metabolismo , Proteínas de Plantas/metabolismo , Tubérculos/crescimento & desenvolvimento , Tubérculos/metabolismo , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/crescimento & desenvolvimento , Plantas Geneticamente Modificadas/metabolismo , Plasmídeos/genética , Plasmídeos/metabolismo , Reação em Cadeia da Polimerase , Regiões Promotoras Genéticas , Interferência de RNA , Solanum tuberosum/metabolismoRESUMO
· Strigolactones (SLs) are a class of phytohormones controlling shoot branching. In potato (Solanum tuberosum), tubers develop from underground stolons, diageotropic stems which originate from basal stem nodes. As the degree of stolon branching influences the number and size distribution of tubers, it was considered timely to investigate the effects of SL production on potato development and tuber life cycle. · Transgenic potato plants were generated in which the CAROTENOID CLEAVAGE DIOXYGENASE8 (CCD8) gene, key in the SL biosynthetic pathway, was silenced by RNA interference (RNAi). · The resulting CCD8-RNAi potato plants showed significantly more lateral and main branches than control plants, reduced stolon formation, together with a dwarfing phenotype and a lack of flowering in the most severely affected lines. New tubers were formed from sessile buds of the mother tubers. The apical buds of newly formed transgenic tubers grew out as shoots when exposed to light. In addition, we found that CCD8 transcript levels were rapidly downregulated in tuber buds by the application of sprout-inducing treatments. · These results suggest that SLs could have an effect, solely or in combination with other phytohormones, in the morphology of potato plants and also in controlling stolon development and maintaining tuber dormancy.
Assuntos
Proteínas de Plantas/genética , Brotos de Planta/crescimento & desenvolvimento , Brotos de Planta/genética , Tubérculos/crescimento & desenvolvimento , Tubérculos/genética , Solanum tuberosum/enzimologia , Solanum tuberosum/genética , Compostos de Benzil/farmacologia , Carotenoides/metabolismo , Clorofila/metabolismo , Dioxigenases/genética , Dioxigenases/metabolismo , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/genética , Regulação Enzimológica da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas/genética , Giberelinas/farmacologia , Lactonas/metabolismo , Lactonas/farmacologia , Fenótipo , Dormência de Plantas/efeitos dos fármacos , Dormência de Plantas/genética , Proteínas de Plantas/metabolismo , Brotos de Planta/efeitos dos fármacos , Caules de Planta/efeitos dos fármacos , Caules de Planta/genética , Caules de Planta/crescimento & desenvolvimento , Tubérculos/efeitos dos fármacos , Purinas/farmacologia , Interferência de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Solanum tuberosum/efeitos dos fármacos , Solanum tuberosum/crescimento & desenvolvimentoRESUMO
Several hormones have been studied for their effect on tuber initiation and development. Until recently, the hormone with the most prominent role in tuber initiation was attributed to GA. Genes involved in GA degradation do exhibit an upregulated profile during early stages of tuber development, leading to a rapid decrease of active GA content, thereby facilitating stolon-tip swelling. While GA is known to be involved in shoot and stolon elongation, the development of the new tuberorgan requires changes in meristem identity and the reorientation ofthe plane of cell division. In other developmental processes, such as embryo patterning, flower development and lateral root initiation auxin plays a key role. Recent evidence on the involvement of auxin in tuber formation was providedby the measurement of auxin content in swelling stolons. Auxin content in the stolon tips increased several fold prior to tuber swelling. In vitro tuberisation experiments with auxin applications support the role of auxin during tuber initiation. Taken together, it is becoming clear that the initiation and induction of tubers in potato is a developmental process that appears to be regulated by a crosstalk between GA and auxin.
Assuntos
Giberelinas/metabolismo , Ácidos Indolacéticos/metabolismo , Tubérculos/crescimento & desenvolvimento , Tubérculos/metabolismo , Solanum tuberosum/crescimento & desenvolvimento , Solanum tuberosum/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Modelos Biológicos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Tubérculos/genética , Solanum tuberosum/genéticaRESUMO
Various transcriptional networks and plant hormones have been implicated in controlling different aspects of potato tuber formation. Due to its broad impact on many plant developmental processes, a role for auxin in tuber initiation has been suggested but never fully resolved. Here, auxin concentrations were measured throughout the plant prior to and during the process of tuber formation. Auxin levels increase dramatically in the stolon prior to tuberization and remain relatively high during subsequent tuber growth, suggesting a promoting role for auxin in tuber formation. Furthermore, in vitro tuberization experiments showed higher levels of tuber formation from axillary buds of explants where the auxin source (stolon tip) had been removed. This phenotype could be rescued by application of auxin on the ablated stolon tips. In addition, a synthetic strigolactone analogue applied on the basal part of the stolon resulted in fewer tubers. The experiments indicate that a system for the production and directional transport of auxin exists in stolons and acts synergistically with strigolactones to control the outgrowth of the axillary stolon buds, similar to the control of above-ground shoot branching.