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Epigenetic regulation of the Qua-Quine Starch neogene during Arabidopsis thaliana development and its impact on starch metabolism

Raphael Ricon de Oliveira
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas. Instituto de Biologia
Defense date:
Examining board members:
Juan Armando Casas Mollano; Marcio Alves Ferreira; Camila Caldana; Jörg Kobarg
Advisor: Michel Georges Albert Vincentz

DNA methylation of the fifth carbon of cytosine is an epigenetic mark that may affect gene expression. The regulation of methylation profiles is important for normal plant development being critical for transposon silencing, imprinting, gametogenesis and early embryo development. However, how methylation of cis regulatory sequences affect the interaction between DNA and developmental associated trans factors to modulate gene expression is poorly understood. Qua-Quine Starch (QQS) is an orphan gene of Arabidopsis thaliana which exhibits several epiallelic forms stably-inherited and their expression levels correlate inversely with the methylation levels at the promoter and 5¿UTR. Through the expression analyses of the GUS reporter gene under the control of a QQS promoter sequence and QQS 5¿UTR in Arabidopsis transgenic lines, we inferred the potential of QQS expression in various organs and at several developmental stages. The GUS activity was detected in meristems, young rosette leaves and pollen where an epigenetic reprogramming of this gene has been described. Contrasting QQS epialleles presented different expression patterns during development. The methylated QQS epiallele (QQSme) showed more pronounced expression differences between leaves, inflorescence tissues and fruit, whereas the demethylated Col*3-2 epiallele presented a more homogeneous expression between this various organs. These results indicate that the methylation level of QQS cis regulatory sequence interacts with developmental-related factors to establish the expression profile of this gene. QQSme expression increases during aging of leaves and was correlated with demethylation. We hypothesized that the QQSme methylation profile could be reprogrammed during leaf development starting from the shoot apical meristem. Such process could be controlled by the DNA glycosilase ROS1, or be passive, as a consequence of the absence or failure in the maintenance mechanisms of the methylation pattern during cell replication. Accordingly, we showed that the QQSme expression is low in samples enriched in meristematic cells and increases progressively with leaf aging and reduction of QQSme methylation levels was observed in older leaves. In some organs, QQS expression variations not correlated with variation in the methylation levels were found. Thus, the results indicate that in addition to DNA methylation developmental associated trans factors are also necessary to modulate QQS expression. The demethylation process of QQSme in old leaves is not totally dependent upon ROS1. However, the levels and pattern of QQS expression in ros1 mutants are different from those in wild-type plants and the analysis of a segregating F2 population coming from selfing of a hybrid between the wild-type and ros1-4 mutant revealed that ROS1 regulates the global expression level of QQS. Therefore, DNA methylation seems to act as traffic lights of binding sites to the trans factors and ROS1 may be important to regulate and/or define QQS epiallelic states. Furthermore, during the reproductive development the expression of QQS is detected in the pollen and correlates with the active demethylation of its locus mediated by DEMETER, which reinforces the fact that QQS is a target of DNA glycosilases. During vegetative development QQS has been described as a negative regulator of starch metabolism. We verified that plants carrying contrasting QQS epialleles accumulate different starch quantities. (AU)

FAPESP's process: 11/06413-0 - Epigenetic regulation of QQS (At3g30720) along Arabidopsis thaliana development and in response to environmental signals
Grantee:Raphael Ricon de Oliveira
Support type: Scholarships in Brazil - Doctorate