THE MAIZE EMPTY PERICARP MUTANTS, A TOOL TO STUDY THE GENETIC CONTROL OF DEVELOPMENT AND THE INTERACTION BETWEEN NUCLEAR AND MITOCHONDRIAL GENOME.
Tesi di Dottorato
Data di Pubblicazione:
2010
Citazione:
THE MAIZE EMPTY PERICARP MUTANTS, A TOOL TO STUDY THE GENETIC CONTROL OF DEVELOPMENT AND THE INTERACTION BETWEEN NUCLEAR AND MITOCHONDRIAL GENOME / D. Gabotti ; Tutor: Gabriella Consonni ; Docente di supporto: Giuseppe Gavazzi ; Coordinatore: Daniele Bassi. Università degli Studi di Milano, 2010 Dec 16. 23. ciclo, Anno Accademico 2010. [10.13130/gabotti-damiano_phd2010-12-16].
Abstract:
The empty pericarp4 (emp4) gene encodes a mitochondrion-targeted PentatricoPeptide Repeat (PPR) protein that is necessary for the correct regulation of mitochondrial gene expression in the endosperm. The two main objectives of this thesis are to understand the role exerted by EMP4 during plant development, and to study the action of emp4 at the molecular level.
Homozygous mutant emp4 embryos are retarded in their development and unable to germinate; therefore to examine the role of the emp4 gene during seedling development homozygous mutant seedlings were obtained from the cultivation of excised immature embryos on a synthetic medium. When exposed to light, after 30 days of culture, 44% of mutant embryos germinated and only few of them produced a seedling. In contrast, in dark condition mutant embryos have a germination rate of 83% and the number of plants that reached the first and the second leaf stage were almost doubled.
A genetic stock carrying an Ac transposon and a double Ds element located on the long arm of chromosome one, where emp4 resides, had been crossed with +/emp4 plants. Chromosome breakages, induced by Ds in somatic tissues, are expected to produce in heterozygous plants clonal sectors hemizygous for the emp4 mutation. Clearly distinguishable yellow sectors were isolated from wild-type green leaves and their hemizygous genotype was confirmed by PCR. Hemyzigous and heterozygous tissues as well as mutant first leaves and primary roots recovered from both light and dark treatment, were analyzed at light microscopy and by TEM analysis.
Typical root anatomy with the peculiar root cell layers was observed in both wild-type and in mutant samples, however in mutant epidermis and hypodermis cell layers were less ordered and alterations in the cell shape were evident, particularly in light. Moreover, comparison between mutant and wild-type root morphology, indicated that mutant roots either grown in the dark or exposed to light were less developed then wild-types and the cell layers epidermis and hypodermis were not properly organized.
All the mesophyll compartments (epidermis, vessels and parenchyma) were clearly detectable in both mutant and wild-type tissues in both conditions. In the dark, mutant tissues were composed by smaller cells with abnormal shapes, moreover in both genotypes, chloroplasts, that were distinguishable in wild-type leaf grown in light treatment, could not be observed. In the light, mutant leaves were smaller in comparison with wild-type and displayed a pale green color. Abnormalities were founded in sections of homozygous mutant plants, like alteration in cell shape and size, a smaller population of chloroplasts and lack of nuclei.
Changes in the subcellular structure were highlighted from the comparison of wild-type and mutant tissues by means of transmission electron microscopy. In emp4 mutant leaves, mitochondria as well as chloroplast populations were significantly reduced and both organelles displayed a less organized structure. In particular, the main alteration were observed in leaf tissues exposed to light while dark-grown tissues seem to be less affected by the effect of emp4 mutation.
Many alterations were detected from the comparison of hemyzigous and heterozygous sectors. Such alterations are similar to those observed in homozygous mutant leaf tissues derived from embryo rescue. Thus, we concluded that emp4 gene is essential to leaf tissues in order to develop and maintain a proper cellular organization. These alterations resemble (for some aspects) in part the macro-autophagy model and in part the model for senescence. Light exposure had a deep effect on cell morphology of emp4 cells, as if a magnification in the senescence process was triggered by this signal, part
Tipologia IRIS:
Tesi di dottorato
Keywords:
maize ; empty pericarp mutant ; mitochondria ; senescence
Elenco autori:
D. Gabotti
Link alla scheda completa:
Link al Full Text: