The Arabidopsis SUCROSE UNCOUPLED‐6 gene is identical to ABSCISIC ACID INSENSITIVE‐4: involvement of abscisic acid in sugar responses

Abstract

SummaryIn plants, sugars act as signalling molecules that control many aspects of metabolism and development. Arabidopsis plants homozygous for the recessive sucrose uncoupled-6 (sun6) mutation show a reduced sensitivity to sugars for processes such as photosynthesis, gene expression and germination. The sun6 mutant is insensitive to sugars that are substrates for hexokinase, suggesting that SUN6 might play a role in hexokinase-dependent sugar responses. The SUN6 gene was cloned by transposon tagging and analysis showed it to be identical to the previously described ABSCISIC ACID INSENSITIVE-4 (ABI4) gene. Our analysis suggests the involvement of abscisic acid and components of the abscisic acid signal transduction cascade in a hexokinase-dependent sugar response pathway. During the plant life cycle, SUN6/ABI4 may be involved in controlling metabolite availability in an abscisic acid-and sugardependent way.

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

“…The isi4/gin1 mutants were found to display ABA-de®cient phenotypes, and their proposed identity as alleles of aba2 is discussed. Our results show that sugar induction of starch biosynthetic genes, like carbohydrate repression of seedling development and concomitant induction of photosynthetic gene expression (ArenasHuertero et al, 2000;Huijser et al, 2000;Laby et al, 2000), depends on ABA signalling. Arenas-Huertero et al (2000) recently suggested that glucose responses were mediated through ABA signalling.…”

“…Two of the isi mutants isolated (isi3 and isi4) were found to be allelic to mutants identi®ed in sugar-sensing screens based on seedling development (Arenas-Huertero et al, 2000;Huijser et al, 2000;Laby et al, 2000). These groups reported that the sun6, sis5 and gin6 mutants were alleles of abscisic acid insensitive4, and that known aba and abi mutants exhibited glucose insensitive phenotypes.…”

“…Mutants in abi4 have now been isolated in a number of genetic screens, all involving selection at the seedling stage. Originally isolated as a mutant germinating in the presence of ABA (Finkelstein et al, 1998), it also shows germination and seedling establishment on high glucose, sucrose and mannose (Arenas-Huertero et al, 2000;Huijser et al, 2000;Laby et al, 2000;this study), and high salinity and osmolarity (Quesada et al, 2000). This suggests that in abi4 mutants, a variety of external stimuli no longer inhibit a program of seedling establishment.…”

“…The prl1 mutation, conferring hypersensitivity to glucose and sucrose, encodes a nuclear WD protein (Ne  meth et al, 1998) and was found to interact with Arabidopsis SNF1-like protein kinases (Bhalerao et al, 1999). Recently it was reported that the sun6 mutant, showing reduced carbohydrate repression of photogene expression during seedling development, encodes the AP2-domain transcription factor ABSCISIC ACID INSENSITIVE4 (ABI4; Huijser et al, 2000). A role for abscisic acid (ABA) signalling in sugar regulation of plant vegetative development was implied by the observation that ABA-de®cient and several ABAinsensitive mutants are insensitive to high levels of glucose and sucrose (Arenas-Huertero et al, 2000;Huijser et al, 2000;Laby et al, 2000).…”

EXORDIUM-LIKE1 Promotes Growth during Low Carbon Availability in Arabidopsis

“…For example, abscisic acid-deficient or abscisic acidinsensitive mutants are Glc insensitive (ArenasHuertero et al, 2000;Huijser et al, 2000;Laby et al, 2000;Cheng et al, 2002). Ethylene overproduction mutants and mutants with constitutive ethylene signaling show reduced responses to high levels of Glc or Suc, whereas ethylene-insensitive mutants are hypersensitive to sugar (Zhou et al, 1998;Cheng et al, 2002).…”