fruit. Rab GTPase enzymes give rise to this control by regulating
vesicle docking through action as a molecular switch [19]. It has
now been shown that there are many related clades of Rabs across
many species throughout nature and these regulate docking with
different parts of the endomembrane system [20e23]. In particular,
the plant RabA GTPase class is deserving of investigation. Plant
species possess an expanded RabA class compared with their
mammalian Rab11 counterparts. In Arabidopsis there are 57 individual
RAB genes of which 26 belong to the RABA class [22].
SlRab11a (formerly LeRab11a), which is orthologous to RABA1a in
Arabidopsis is associated with the TGN and dominant negative
versions of the SlRab11a gene showed inhibited exocytosis of
secreted GFP [24]. In addition, an antisense SlRab11a construct
reduced tomato fruit softening, producing firmer fruit in comparison
to the Ailsa Craig wild type (ACþþ) and reduced levels of
several cell wall modifying enzymes in the fruit [25]. However, as
well as enzymes, many other compounds are transported through
the TGN to the plasma membrane and the apoplast. Therefore, we
decided to analyse other possible components of the cell wall that
might have been affected by inhibition of Rab11 activity.
2. Results
2.1. Confirmation of G4 antisense homozygous lines
Wild type and G4 antisense lines [25] were grown from seed and
PCRwas undertaken to confirm the presence of the antisense Rab11a
construct in the fruit. The results are shown in Supplementary
Fig. S1. As a confirmation of the expression of the antisense
phenotype, fruit was harvested at fixed times during ripening and
firmness was assessed using texture analysis (Supplementary
Fig. S2). This confirmed the slow softening phenotype of the G4
line. Photographs of fruit at the 40 day post breaker stage further
confirm this phenotype (Supplementary Fig. S3). At this point the
ACþþ tomatoes had lost their smooth structure and had cracked
exocarps which accounts for the infection shown.
2.2. mRNA expression profiling of SlRab11a during fruit
development and ripening
The expression of SlRab11a has only previously been determined
during ripening and only by northern blot. We determined the
expression profile for SlRab11a in the wild type during both fruit
development and ripening using quantitative real-time PCR and
specific primers. Fig. 1 shows that the mRNA level was at its
maximum at 15 days-post-anthesis (15 dpa) which was the earliest