Impaired sucrose‐induction mutants reveal the modulation of sugar‐induced starch biosynthetic gene expression by abscisic acid signalling

Abstract

SummaryPlants both produce and utilize carbohydrates and have developed mechanisms to regulate their sugar status and co-ordinate carbohydrate partitioning. High sugar levels result in a feedback inhibition of photosynthesis and an induction of storage processes. We used a genetic approach to isolate components of the signalling pathway regulating the induction of starch biosynthesis. The regulatory sequences of the sugar inducible ADP-glucose pyrophosphorylase subunit ApL3 were fused to a negative selection marker. Of the four impaired sucrose induction (isi) mutants described here, two (isi1 and isi2) were speci®c to this screen. The other two mutants (isi3 and isi4) showed additional phenotypes associated with sugarsensing screens that select for seedling establishment on high-sugar media. The isi3 and isi4 mutants were found to be involved in the abscisic acid signalling pathway. isi3 is allelic to abscisic acid insensitive4 (abi4), a gene encoding an Apetala2-type transcription factor; isi4 was found to be allelic to glucose insensitive1 (gin1) previously reported to reveal cross-talk between ethylene and glucose signalling. Here we present an alternative interpretation of gin1 as an allele of the ABA-de®cient mutant aba2. Expression analysis showed that ABA is unable to induce ApL3 gene expression by itself, but greatly enhances ApL3 induction by sugar. Our data suggest a major role for ABA in relation to sugar-signalling pathways, in that it enhances the ability of tissues to respond to subsequent sugar signals.

Analysis of a Sugar Response Mutant of Arabidopsis Identified a Novel B3 Domain Protein That Functions as an Active Transcriptional Repressor

“…Given that the Spo min promoter is induced by both sugars and ABA and that sugar enhances the endogenous level of ABA (Arenas-Huertero et al, 2000;Rook et al, 2001), the high-level expression of Spo min in the hsi2 mutant could be due to a high endogenous level of ABA or to altered starch metabolism. However, the level of ABA in leaves of the hsi2 plants and its increase after treatment with Suc were similar to those in leaves of the sGsL plants (Fig.…”

“…Genetic analyses of sugar signaling mutants of Arabidopsis (Arabidopsis thaliana), obtained by genetic screen based on inhibition of germination and early seedling development by sugars, revealed a close link between sugar signaling and the production of ethylene and abscisic acid (ABA; for review, see Gazzarrini and McCourt, 2001;Rook and Bevan, 2003). In addition, direct screening based on sugar-responsive expression of endogenous genes or transgenes with reporters also resulted in identification of mutants with altered sugar-responsive gene expression (Dijkwel et al, 1997;Martin et al, 1997;Mita et al, 1997aMita et al, , 1997bRook et al, 2001; Baier et al, 2004). In general, these mutants affected the expression of a subset of sugar-regulated genes, and mutation either diminished or enhanced the sugarresponsive expression of the target gene.…”

Seed dormancy and germination

“…Mutants that were insensitive to the inhibiting effect of glucose and sucrose on early seedling development were isolated by several groups and identified ABA deficient mutants (i.e. aba2/isi4/gin1/sis4 and aba3/gin5) and ABA insensitive4 (abi4/sun6/isi3/gin6/sis5) as sugar insensitive (Arenas-Huertero et al, 2000; Huijser et al, 2000; Laby et al, 2000;Rook et al, 2001). The fact that ABI4 encodes an AP2 domain containing transcription factor that binds a CE1-like element present in many ABA and sugar regulated promoters (Finkelstein et al, 1998;Niu et al, 2002; Acevedo-Hernandez et al, 2005) linked sugar regulation to ABA signalling.…”

Hypobaric Biology: Arabidopsis Gene Expression at Low Atmospheric Pressure

“…Ozturk et al, 2002). Examples from cluster A2 include ABI2 (Chak et al, 2000), the APL3 subunit of ADP-Glc pyrophosphorylase (Weber et al, 1995;Rook et al, 2001), LEAs (e.g. Siddiqui et al, 1998;Kim et al, 2002), dehydrins and rab-like proteins (e.g.…”