Sucrose Control of Phytochrome A Signaling in Arabidopsis

Abstract

The expression of the Arabidopsis plastocyanin (PC) gene is developmentally controlled and regulated by light. During seedling development, PC gene expression is transiently induced, and this induction can be repressed by sucrose. In transgenic seedlings carrying a PC promoter-luciferase fusion gene, the luciferase-induced in vivo luminescence was similarly repressed by sucrose. From a mutagenized population of such transgenic seedlings, we selected for mutant seedlings that displayed a high luminescence leve1 when grown on a medium with 3% sucrose. This screening of mutants resulted in the isolation of several sucrose-uncoupled (sun) mutants showing reduced repression of luminescence by sucrose. Analysis of the sun mutants revealed that the accumulation of PC and chlorophyll a/b binding protein (CAB) mRNA was also sucrose uncoupled, although the extent of uncoupling varied. The effect of sucrose on far-red light high-irradiance responses was studied in wild-type, sunl, sun6, and sun7 seedlings. In wild-type seedlings, sucrose repressed the far-red light-induced cotyledon opening and inhibition of hypocotyl elongation. sun7 seedlings showed reduced repression of these responses. Sucrose also repressed the far-red light-induced block of greening in wild-type seedlings, and both sun6 and sun7 were affected in this response. The results provide evidence for a close interaction between sucrose and light signaling pathways. Moreover, the sun6 and sun7 mutants genetically identify separate branches of phytochrome A-dependent signal transduction pathways.

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

“…This is similar to the position described for the sucrose-uncoupled6 (sun6, Dijkwel et al, 1997) mutant that was recently reported to encode ABI4 , an Apetala2-type transcription factor originally isolated as the abscisic acidinsensitive mutant abi4 (Finkelstein et al, 1998). Alleles of abi4 have also been identi®ed in sugar-sensing screens selecting for vegetative development on high-sugar media (Arenas-Huertero et al, 2000;Laby et al, 2000).…”

An Arabidopsis mutant showing reduced feedback inhibition of photosynthesis

“…Mutants which showed no repression of PC promoter activity by sucrose at the seedling stage were isolated (Dijkwel et aL, 1997). Three of them, sun I-2, sun6 and sun7, were backcrossed twice to the PC-LUC plants and retained their phenotype, sunl-2 and sun7 displayed a higher luciferase activity than the wild-type PC-LUC seedlings whereas sun6 plants had luminescence levels comparable to those of the PC-LUC plants (Dijkwel etal., 1997).…”

“…A total of 17 such mutant lines were obtained and three of these were selected for detailed analysis. Genetic analysis shows that these sun1, sun6, sun7 mutations represent recessive Mendelian loci (Dijkwel et aL, 1997). In these mutants, the endogenous PC, CAB and RBCS steady-state mRNA levels were also sucrose-uncoupled at the seedling stage.…”

Sucrose and Cytokinin Modulation of WPK4, a Gene Encoding a SNF1-Related Protein Kinase from Wheat

“…Recent studies have suggested that hexokinase, which was postulated to play an important role in sugar sensing in yeast (Ma et al, 1989;Rose et al, 1991), could be responsible for sensing sugars to repress a number of plant genes (Graham et al, 1994;Jang and Sheen, 1994). However, there are some examples of hexoseindependent changes in gene expression (Wenzler et al, 1989;Dijkwel et al, 1997) and in proton-Suc symporter activity (Chiou and Bush, 1998). Thus, mechanisms by which sugar is sensed and sugar signals are transduced are not completely clear yet.…”