Final Activity Report Summary - ENDOREPTOM (Functional analysis of endoreduplication during tomato fruit development)
The control of the two developmental processes that are cell division and cell expansion is a crucial determinant of fruit size, an essential criterion for final fruit quality. Indeed, in many species the variation in final fruit size has been attributed to differences in cell number rather than cell size. The cell number is thus a key component in the determination of tomato fruit size. According to the fruit developmental scheme, genes coding for cell division regulators such as cell cycle proteins may represent relevant candidate genes which could be involved in the molecular mechanisms governing fruit organogenesis. Among these regulators, the WEE1 protein kinase is involved in the control of cell size checkpoint of the cell cycle in fission yeast, preventing the cell to engage into mitosis unless it reaches a minimal cell mass. This project aimed at investigating the role for WEE1 in higher plant cell size determination.
In plants WEE1 is encoded by a single gene which makes it an interesting candidate to manipulate in planta, and especially in fruits. We thus investigated the regulation of the WEE1 gene in tomato. First we cloned the complete genomic and cDNA sequences for WEE1. We then studied the expression profile of the WEE1 gene as determined by semi-quantitative RT-PCR in whole fruits and in the dissected tissues of the fruit at the various stages of fruit development and in the different vegetative organs of tomato plant. These data indicated that the WEE1 gene expression was enhanced during the cell expansion phase of tomato fruit development, especially within the gel tissue when mitosis is hampered and cell polyploidisation through endoreduplication is triggered. To perform a functional analysis, transgenic tomato plants were generated in which the expression of WEE1 is inhibited by producing antisense RNA. Inhibiting the WEE1 expression resulted in an alteration of plant size, fruit size and cell size, together with a decrease in cell polyploidisation. Our data bring further knowledge about the control of cell cycle, cell size and endoreduplication in higher plant cells.
In plants WEE1 is encoded by a single gene which makes it an interesting candidate to manipulate in planta, and especially in fruits. We thus investigated the regulation of the WEE1 gene in tomato. First we cloned the complete genomic and cDNA sequences for WEE1. We then studied the expression profile of the WEE1 gene as determined by semi-quantitative RT-PCR in whole fruits and in the dissected tissues of the fruit at the various stages of fruit development and in the different vegetative organs of tomato plant. These data indicated that the WEE1 gene expression was enhanced during the cell expansion phase of tomato fruit development, especially within the gel tissue when mitosis is hampered and cell polyploidisation through endoreduplication is triggered. To perform a functional analysis, transgenic tomato plants were generated in which the expression of WEE1 is inhibited by producing antisense RNA. Inhibiting the WEE1 expression resulted in an alteration of plant size, fruit size and cell size, together with a decrease in cell polyploidisation. Our data bring further knowledge about the control of cell cycle, cell size and endoreduplication in higher plant cells.