MYB transcription factors in Arabidopsis

http://nhjy.hzau.edu.cn/kech/ssyy/pdf/drought/4.PDF

Photosynthesis under drought and salt stress: regulation mechanisms from whole plant to cell

Cold, salinity and drought stresses: an overview.

Abscisic acid (ABA) regulates many agronomically important aspects of plant development, including the synthesis of seed storage proteins and lipids, the promotion of seed desiccation tolerance and dormancy, and the inhibition of the phase transitions from embryonic to germinative growth and from

/pdf/abscisic-acid-signaling-in-seeds-and-seedlings-21b3w9tc2t.pdf

Abscisic Acid Signaling in Seeds and Seedlings

Sugars not only fuel cellular carbon and energy metabolism but also play pivotal roles as signaling molecules. The experimental amenability of yeast as a unicellular model system has enabled the discovery of multiple sugar sensors and signaling pathways. In plants, different sugar signals are generated by photosynthesis and carbon metabolism in source and sink tissues to modulate growth, development, and stress responses. Genetic analyses have revealed extensive interactions between sugar and plant hormone signaling, and a central role for hexokinase (HXK) as a conserved glucose sensor. Diverse sugar signals activate multiple HXK-dependent and HXKindependent pathways and use different molecular mechanisms to control transcription, translation, protein stability and enzymatic activity. Important and complex roles for Snf1-related kinases (SnRKs), extracellular sugar sensors, and trehalose metabolism in plant sugar signaling are now also emerging.

https://molbio.mgh.harvard.edu/sheenweb/reprints/ARPB06sugar.pdf

Sugar Sensing and Signaling in Plants: Conserved and Novel Mechanisms

The control of plant anthocyanin accumulation is via transcriptional regulation of the genes encoding the biosynthetic enzymes. A key activator appears to be an R2R3 MYB transcription factor. In apple fruit, skin anthocyanin levels are controlled by a gene called MYBA or MYB1, while the gene determining fruit flesh and foliage anthocyanin has been termed MYB10. In order to further understand tissue-specific anthocyanin regulation we have isolated orthologous MYB genes from all the commercially important rosaceous species. We use gene specific primers to show that the three MYB activators of apple anthocyanin (MYB10/MYB1/MYBA) are likely alleles of each other. MYB transcription factors, with high sequence identity to the apple gene were isolated from across the rosaceous family (e.g. apples, pears, plums, cherries, peaches, raspberries, rose, strawberry). Key identifying amino acid residues were found in both the DNA-binding and C-terminal domains of these MYBs. The expression of these MYB10 genes correlates with fruit and flower anthocyanin levels. Their function was tested in tobacco and strawberry. In tobacco, these MYBs were shown to induce the anthocyanin pathway when co-expressed with bHLHs, while over-expression of strawberry and apple genes in the crop of origin elevates anthocyanins. This family-wide study of rosaceous R2R3 MYBs provides insight into the evolution of this plant trait. It has implications for the development of new coloured fruit and flowers, as well as aiding the understanding of temporal-spatial colour change.

/pdf/an-r2r3-myb-transcription-factor-associated-with-regulation-3eochh883k.pdf

An R2R3 MYB transcription factor associated with regulation of the anthocyanin biosynthetic pathway in Rosaceae

Background

The control of plant anthocyanin accumulation is via transcriptional regulation of the genes encoding the biosynthetic enzymes. A key activator appears to be an R2R3 MYB transcription factor. In apple fruit, skin anthocyanin levels are controlled by a gene called MYBA or MYB1, while the gene determining fruit flesh and foliage anthocyanin has been termed MYB10. In order to further understand tissue-specific anthocyanin regulation we have isolated orthologous MYB genes from all the commercially important rosaceous species.

Results

We use gene specific primers to show that the three MYB activators of apple anthocyanin (MYB10/MYB1/MYBA) are likely alleles of each other. MYB transcription factors, with high sequence identity to the apple gene were isolated from across the rosaceous family (e.g. apples, pears, plums, cherries, peaches, raspberries, rose, strawberry). Key identifying amino acid residues were found in both the DNA-binding and C-terminal domains of these MYBs. The expression of these MYB10 genes correlates with fruit and flower anthocyanin levels. Their function was tested in tobacco and strawberry. In tobacco, these MYBs were shown to induce the anthocyanin pathway when co-expressed with bHLHs, while over-expression of strawberry and apple genes in the crop of origin elevates anthocyanins.

Conclusions

This family-wide study of rosaceous R2R3 MYBs provides insight into the evolution of this plant trait. It has implications for the development of new coloured fruit and flowers, as well as aiding the understanding of temporal-spatial colour change.

Sugar-mediated regulation of gene expression is a mechanism controlling the expression of many different plant genes. In this review, a compilation of the genes encoding photosynthetic proteins, subject to this mode of regulation, is presented. Several groups have devised different screening strategies to obtain Arabidopsis mutants in sugar sensing and signalling. An overview of these strategies has been included. Sugar-mediated regulation of gene expression is thought to require the hexokinase (HXK) protein. It has previously been shown that one such sugar, mannose, is capable of blocking germination in Arabidopsis. This inhibition is also mediated by HXK and occurs in the low millimolar concentration range. Here, the use of germination on mannose as an effective screening strategy for putative sugar sensing and signalling mutants is reported. T-DNA- and EMS-mutagenized collections were used to isolate 31 mannose-insensitive germination (mig) mutants. With the use of these mutants, a comparison between this screen and other existing sugar-sensing screens is presented.

Photosynthesis, sugars and the regulation of gene expression.

Summary
The Arabidopsis bZIP transcription factor gene ATB2 has been shown previously to be expressed in a light-regulated and tissue-specific way. Here we describe the precise localization of ATB2 expression, using transgenic lines containing an ATB2 promoter–GUS reporter gene construct. The observed expression pattern suggests a role for ATB2 in the control of processes associated with the transport or utilization of metabolites. Remarkably, expression of the ATB2–GUS reporter gene construct was specifically repressed by sucrose. Other sugars, such as glucose and fructose, alone or in combination, were ineffective. Repression was observed at external sucrose concentrations exceeding 25 mM. Transcript levels of both the endogenous ATB2 gene and the ATB2–GUS reporter gene were not repressed by sucrose, suggesting that sucrose affects mRNA translation. This translational regulation involves the ATB2 leader sequence because deletion of the leader resulted in loss of sucrose repression. Our results provide evidence for a sucrose-specific sugar sensing and signalling system in plants.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313X.1998.00205.x

Sucrose‐specific signalling represses translation of the Arabidopsis ATB2 bZIP transcription factor gene

In 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 sugar-dependent way.

A.J. Kortstee

Papers

An R2R3 MYB transcription factor associated with regulation of the anthocyanin biosynthetic pathway in Rosaceae

An R2R3 MYB transcription factor associated with regulation of the anthocyanin biosynthetic pathway in Rosaceae

Photosynthesis, sugars and the regulation of gene expression.

Sucrose‐specific signalling represses translation of the Arabidopsis ATB2 bZIP transcription factor gene

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