RESUMO
Transfer cells (TCs) trans-differentiate from differentiated cells by developing extensive wall ingrowths that enhance plasma membrane transport of nutrients. Here, we investigated transcriptional changes accompanying induction of TC development in adaxial epidermal cells of cultured Vicia faba cotyledons. Global changes in gene expression revealed by cDNA-AFLP were compared between adaxial epidermal cells during induction (3 h) and subsequent building (24 h) of wall ingrowths, and in cells of adjoining storage parenchyma tissue, which do not form wall ingrowths. A total of 5795 transcript-derived fragments (TDFs) were detected; of these, 264 TDFs showed epidermal-specific changes in gene expression and a further 207 TDFs were differentially expressed in both epidermal and storage parenchyma cells. Genes involved in signalling (auxin/ethylene), metabolism (mitochondrial; storage product hydrolysis), cell division, vesicle trafficking and cell wall biosynthesis were specifically induced in epidermal TCs. Blockers of auxin action and vesicle trafficking inhibited ingrowth formation and marked increases in cell division accompanied TC development. Auxin and possibly ethylene signalling cascades induce epidermal cells of V. faba cotyledons to trans-differentiate into TCs. Trans-differentiation is initiated by rapid de-differentiation to a mitotic state accompanied by mitochondrial biogenesis driving storage product hydrolysis to fuel wall ingrowth formation orchestrated by a modified vesicle trafficking mechanism.
Assuntos
Transdiferenciação Celular/genética , Cotilédone/citologia , Cotilédone/genética , Regulação da Expressão Gênica de Plantas , Epiderme Vegetal/citologia , Epiderme Vegetal/genética , Vicia faba/genética , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , Divisão Celular/efeitos dos fármacos , Transdiferenciação Celular/efeitos dos fármacos , Parede Celular/efeitos dos fármacos , Parede Celular/metabolismo , Células Cultivadas , Cotilédone/efeitos dos fármacos , Cotilédone/ultraestrutura , DNA Complementar/genética , Etilenos/farmacologia , Perfilação da Expressão Gênica , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas/genética , Ácidos Indolacéticos/farmacologia , Especificidade de Órgãos/efeitos dos fármacos , Especificidade de Órgãos/genética , Epiderme Vegetal/efeitos dos fármacos , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Biossíntese de Proteínas/efeitos dos fármacos , RNA de Plantas/isolamento & purificação , Transcrição Gênica/efeitos dos fármacos , Vicia faba/citologia , Vicia faba/efeitos dos fármacos , Vicia faba/ultraestruturaRESUMO
Correlative physiological evidence suggests that membrane transport into storage parenchyma cells is a key step in determining hexose levels accumulated in tomato (Lycopersicon esculentum Mill.) fruit (Ruan et al. 1997). Expression of three previously identified hexose transporter genes (LeHT1, 2 and 3) demonstrated that LeHT3, and to a lesser extent LeHT1, are the predominant transporters expressed in young fruit (10 d after anthesis; DAA). Expression of both transporters dropped sharply until 24 DAA, after which only LeHT3 expression remained at detectable levels through to fruit ripening. LeHT2 was not expressed substantially until the onset of fruit ripening. For fruit at both 10 and 30 DAA, LeHT3 transcripts were detected in storage parenchyma cells of the outer pericarp tissue, but not in vascular bundles or the first layer of parenchyma cells surrounding these bundles. In contrast to LeHT gene expression, hexose transporter protein levels were maximal between 20 and 30 DAA, which corresponded to the period of highest hexose accumulation. The delayed appearance of transporter protein is consistent with some form of post-transcriptional regulation. Based on these analyses, LeHT3 appears to be responsible for the rapid hexose accumulation in developing tomato fruit.