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| Author(s): |
Thais Rezende e Silva Figueira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia |
| Defense date: | 2007-02-28 |
| Examining board members: |
Paulo Arruda;
José Andrés Yunes;
Gonçalo Amarante Guimarães Pereira;
Maria Helena de Souza Goldman;
Ricardo Antunes Azevedo;
Maria Fatima Grossi de Sa
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| Advisor: | Paulo Arruda |
| Abstract | |
The sequencing of ESTs (expressed sequence tags) and its organization in databases constitute powerful tools to identify genes of interest in certain tissues and/or cell types. In this work we have created a database of ESTs expressed in diverse maize tissues called MAIZEST. MAIZEST contains 227,431 ESTs coming from over 30 different maize tissues, 64,357 of which coming from developing endosperm. The analysis of MAIZEST database leaded to the identification of 4,032 transcripts preferentially expressed in endosperm, and its annotation revealed a great variety of new genes involved in endosperm metabolism and development. We used the information of the genes encoding the maize storage protein, zein, to comparre with the storage protein genes from sorghum and sugarcane. Genetic and molecular evolution studies have suggested that maize is the product of a tetraploid event which occurred by the interspecific hybridisation of two n = 5 ancestors. It has been proposed that maize may have originated through a segmental allotetraploid event occurred at 11.5 Mya or by a single duplication event occurred about 4.8 Mya. However, the progenitors of the allotetraploid have not as yet been identified. Here we show that one of the progenitors belongs to the saccharum lineage from which modern sugarcane originates. Comparing patterns of the seed storage protein, prolamins, of maize, sorghum and sugarcane, a striking similarity was found between maize and sugarcane. Prolamins, which accumulate in the endosperm of cereal seeds, can be grouped into structurally distinct classes named a-, ß-, ?- and d-prolamins. Almost all prolamin classes are present in maize, sorghum and sugarcane, but in maize there are two molecular weight distinct classes of a-prolamins, the 22 KD and the 19 KD a-zeins. Sorghum possesses only the 22 KD a-kafirin while sugarcane possesses both the 22KD and the 19 KD a-prolamins, which we called caneins. Alignment of the 22 and the 19 KD amino acid sequences revealed that both the 19 KD a-zein and the 19 KD a-canein lack the 6th a-helices domain from the 10 a-helices domains found in the 22 KD a-prolamins. Since the 22 KD a-prolamins are present in sorghum and in the more ancient Andropogoneae species Coix, we postulate that the 19 KD a-prolamins originated, by a deletion of the 6th a-helices domain of the 22 KD a-prolamins, in the saccharum lineage. Saccharum and sorghum diverged about 5-9 Mya, when only the 22 KD a-prolamins existed. The 19KD a-canein originated after this divergence. Therefore, maize inherited the 19KD a-zein from saccharum after the interspecific hybridisation between saccharum and another n = 5 Andropogoneae progenitor (AU) | |