Angeles nÚÑez, Juan Gabriel (2009) Study of sucrose synthase in arabdopsis seed : lacalization, regulation and function. PhD thesis Biologie végétale, INRA/AgroParisTech, UMR204, Laboratoire de Biologie des Semences, Institut Jean-Pierre Bourgin, RD10, 78026 Versailles Cedex, France, AgroParistech 2008AGPT0065 p.140.

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Abstract

Sucrose synthase (SUS) is a key enzyme in sucrose metabolism. This enzyme catalysis the reversible conversion of sucrose

and UDP to UDP-glucose and fructose, which are both used in multiple biochemical pathways. The Arabidopsis genome

contains six sucrose synthase genes. A member of this family (SUS2) is strongly and specifically expressed in Arabidopsis

seeds during the maturation phase, corresponding to reserve accumulation period. Total SUS activity reached a peak during

seed maturation, at about 15 days after flowering (DAF), which corresponds approximately to the middle of this stage. This

activity pattern fitted well with SUS2 mRNA abundance, although we cannot exclude the presence of other SUS isoform

activities, such as SUS3, in seeds at late maturation. Using specific antibodies we have shown that, SUS2 is localised in the

embryo, endosperm and seed coat with differential patterns. During the maturation phase, the SUS2 protein was mainly colocalised

with plastids in the embryo. This result is consistent with the hypothesis that SUS2 association with the plastid may

play a role in channelling of sucrose metabolism to G-6-P or PEP, both carbon compounds which enter the plastids enabling

starch or lipid synthesis. Indeed, the regulation of SUS2 and SUS3 expression was investigated during seed development for

wild type (WT) and for seed maturation mutants (i.e. lec2-4, fus3-4 and abi3). The accumulation patterns of SUS mRNA and

protein, as well as total activity, were strongly affected in these mutants during seed development. We showed that the

expression of the SUS2 promoter was induced in planta by sugar (glucose, sucrose and trehalose) and that the expressions of

SUS2 and SUS3 promoters are redundantly regulated by LEC2 and FUS3 during the maturation phase. Last, a functional

analysis was carried out in developing seeds, using biochemical characterisation and metabolite profiling of one sus1, two

sus2 and two sus3 alleles. The results obtained outlined the importance of these SUS isoforms for sucrose metabolism in

developing seeds of Arabidopsis.

Table of content

2. localisation de la proteine sus2…………………………………………. 19

3. rÉgulation de sus2 et s u s 3 par des facteurs de la

transcription………………………………………………………………………… 33

4. implication des saccharose synthases dans le mÉtabolisme

carbonÉ………………………………………………………………………………… 65

5. discussion gÉnÉrale ……………………………………………………………. 94

6. matÉriels et mÉthodes……………………………………………………… .102

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