Role of HY5 in abscisic acid response in seeds and seedlings

Abstract

response in late embryogenesis-abundant (LEA) gene expression, seed germination, seedling establishment and root growth; (2) HY5 mediates these ABA responses partly by regulating the transcription of the seed/seedling-specific ABA signaling regulator ABI5, (3) ABA specifically enhances HY5 binding to the ABI5 chromatin and; (4) ABI5 sensitizes light repression of hypocotyl elongation. These results raise interesting questions on the interaction of light signaling and ABA signaling and its potential significance in plant response to the environment. HY5 Controls the Expression of ABI5 and ABI5-Targeted GenesThe Arabidopsis HY5 is a positive regulator of seedling photomorphogenesis downstream of diverse photoreceptors. 5-7 HY5 encodes a transcription factor of the basic leucine zipper (bZIP) domain family and controls the expression of many light-responsive genes. The ABI5 locus also encodes a bZIP transcription factor whose accumulation inhibits seed germination and early seedling establishment. 8,9 ABI5 is expressed during seed maturation, seed germination and young seedling stages. Its expression pattern partly overlaps with that of HY5. Both HY5 protein and ABI5 protein are also subjected to proteolysis during the early seedling stage. These observations suggest that HY5 regulation of ABI5 may occur within a restricted developmental window and that there must be other factors controlling the activation of ABI5 by HY5. Indeed, in tobacco BY-2 protoplasts, we did not find clear activation of ABI5 promoter-driven reporter gene by HY5. This indicates that seed or early seedling-specific factors such as ABI3, LEC1 and FUS3 9-13 are also needed for ABI5 activation. Among others, ABI3 was previously suggested to act upstream of ABI5. 11,14 Nonetheless, in our yeast two-hybrid assays, HY5 did not physically interact with ABI3 (Chen H and Xiong L, unpublished), suggesting that these two components may not be in physical contact with one another if they are within a common ABI5 transcriptional activation complex. Further identification of the components in this complex will be important for revealing the signaling network controlling seed development and seed germination.Similar to ABI5, the downstream target genes of ABI5 may also be tightly regulated. Recent microarray experiments with the abi5 as well as hy5 mutants have identified genes potentially regulated by these transcription factors (reviewed in refs. 15 and 16). However, the low level of transcript abundance for some of these genes in seedlings and the sensitivity of their regulation to developmental stages and tissue types make it difficult to interpret some of the data obtained in these microarray assays. While the transcript levels for Light affects many aspects of plant development including seed germination, phototropism, de-etiolation and flowering. 1 Light regulates these processes at least partly through its regulation of the metabolism and signal transduction of phytohormones. Experimental evidence has indicated that classic plant growth hormones, in...

Karrikins enhance light responses during germination and seedling development in Arabidopsis thaliana

“…1C and 2), we investigated the role of HY5 in seed responses to karrikins. Although hy5-1 seed exhibited reduced dormancy, consistent with a recent report (44), its germination was significantly responsive to karrikins ( Fig. S4 A and B).…”

Genetic interaction of two abscisic acid signaling regulators, HY5 and FIERY1, in mediating lateral root formation

“…10,[17][18][19][20] Previously, we reported that HY5, a well-characterized component in the light signal transduction pathway, also mediates ABA response during seed germination and lateral root development. 21,22 Using the enhanced light response as a phenotype, we conducted a genetic screen and isolated fry1 suppressors with reduced light sensitivity. 20 Map-based cloning of several of these suppressors identified that phyB and hy1 mutant alleles were among the suppressors of fry1 light sensitivity.…”

OsbZIP48, a HY5 Transcription Factor Ortholog, Exerts Pleiotropic Effects in Light-Regulated Development

“…In fact, besides Arabidopsis, the overexpression transgenics of the full-length AtHY5 orthologs in the same organism have not been raised, and that makes it difficult for us to conclude whether full-length HY5 overexpression causes semidwarfism only in rice (this study) or in other organisms too. AtHY5 is known to be involved in auxin, GA, cytokinin, ABA, ethylene, and strigolactone signaling; while it represses ethylene, GA, and auxin signaling, it promotes ABA signaling (Cluis et al, 2004;Vandenbussche et al, 2007;Alabadí et al, 2008;Chen and Xiong, 2008;Li et al, 2011b;Yu et al, 2013). In this study too, the expression of genes associated with the biosynthesis of GA, jasmonic acid, ethylene, and brassinosteroid as well as cytokinin glucosylation was altered in OsbZIP48 OE transgenics.…”