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Identifier

000364480

Title

Ο ρόλος του φωτός και της φωτοσύνθεσης στο μηχανισμό της RNA σίγησης στα φυτά

Alternative Title

Τhe role of light and photosynthesis in the RNA silencing mechanism in plants

Author

Κωτάκης, Χρήστος

Thesis advisor

Κοτζαμπάσης, Κυριάκος
Καλαντίδης, Κρίτων

Abstract

‘RNA silencing’ refers collectively to diverse RNA-based processes that all result in sequence-speciﬁc inhibition of gene expression, at the mRNA level (Brodersen and Voinnet, 2006). It has been previously shown that environmental stimuli affect the RNA silencing mechanism in plants (Meza et al., 2001; Yoo et al., 2004). Here, the effect of light quantity was studied in the initiation and systemic spread of RNA silencing signal in plants. In the present study, we found that high light intensity significantly affects positively the induction and systemic spread of sense post-transcriptional gene silencing, in transgenic N. benthamiana plants. Although a moderate increase in the amount of siRNAs was detected in silenced parts, we found that HL has a negative effect on the steady state levels of transgene mRNAs in silenced and non-silenced parts. Also, we monitored the expression profile of six silencing related genes in different lines or silencing states treated with HL and LL. Only DCL4 displayed a light responsive profile in all the cases studied including wt plants. DCL3 and RDR6 were highly or moderately induced under HL provided that silencing was initiated in local or distant parts of the same plant. Next, we followed a reverse genetics approach, in order to uncover a possible mechanistic link between light and silencing. The corresponding experiments indicated that DCL4 suppression but not this of DCL3, results in the neutralisation of altered difference between HL and LL silencing frequencies. This finding underlying a possible role in signal perception by DCL4 concerning post-transcriptional gene silencing and light intensity interaction. The differential response of RNA silencing to variations of light intensity seems to be functionally correlated with the photoadaptive status of photosynthetic apparatus. According to our bioenergetic data, the structure and function of the photosynthetic machinery are changed in tissues undergoing silencing. The photosynthetic metabolism under silencing conditions is described by an increased capacity for non-photochemical quenching, followed by an increment to PSI/PSII activity. The decreased plastoquinone pool in silenced tissues maybe act as a signal for the modified transcriptional stoichiometry of photosystems when RNA silencing mechanism is activated. As a consequence, cyclic electron flow around PSI is accelerated in this type of tissues, providing additional ATP molecules in cells where RNA silencing is maintained. It is known that the biochemical pathway of RNA silencing is ATP-dependent. Plants grown under high light conditions, are characterised by higher availability of ATP pools in comparison to low light grown plants. Hence, it is possible one part of this energetic equivalents to be related with the increased frequency of silencing events as well as with the overall RNA silencing efficiency and establishment in HL conditions.

Language

Greek

Subject

ATP (Adenosine triphosphate)

Cyclic electron flow

Kυκλική ροή ηλεκτρονίων

Light intensity

Mετα-μεταγραφική γονιδιακή σίγηση

Post-transcriptional gene silencing

Transgenic plants

mRNA (Messenger RNA)

Ένταση φωτισμού