MYB transcription factors in Arabidopsis

Three major groups of pigments, the betalains, the carotenoids, and the anthocyanins, are responsible for the attractive natural display of flower colors. Because of the broad distribution of anthocyanins (synthesized as part of the flavonoid pathway) among the flowering plants, their biosynthesis and regulation are best understood. However, over the past few years, significant progress has been made in understanding the synthesis and participation of carotenoids (derived from isoprenoids) and betalains (derived from tyrosine) in flower pigmentation. These three families of pigments play important ecological functions, for example in the attraction of pollinating animals. Anthocyanins in particular have also been the target of numerous biotechnological efforts with the objective of creating new, or altering the properties of existing, coloring compounds. The focus of this review is to examine the biosynthesis, regulation, and contribution to flower coloration of these three groups of pigments.

The genetics and biochemistry of floral pigments

The expansion of gene families encoding regulatory proteins is typically associated with the increase in complexity characteristic of multi-cellular organisms. The MYB and basic helix-loop-helix (bHLH) families provide excellent examples of how gene duplication and divergence within particular groups of transcription factors are associated with, if not driven by, the morphological and metabolic diversity that characterize the higher plants. These gene families expanded dramatically in higher plants; for example, there are approximately 339 and 162 MYB and bHLH genes, respectively, in Arabidopsis, and approximately 230 and 111, respectively, in rice. In contrast, the Chlamydomonas genome has only 38 MYB genes and eight bHLH genes. In this review, we compare the MYB and bHLH gene families from structural, evolutionary and functional perspectives. The knowledge acquired on the role of many of these factors in Arabidopsis provides an excellent reference to explore sequence-function relationships in crops and other plants. The physical interaction and regulatory synergy between particular sub-classes of MYB and bHLH factors is perhaps one of the best examples of combinatorial plant gene regulation. However, members of the MYB and bHLH families also interact with a number of other regulatory proteins, forming complexes that either activate or repress the expression of sets of target genes that are increasingly being identified through a diversity of high-throughput genomic approaches. The next few years are likely to witness an increasing understanding of the extent to which conserved transcription factors participate at similar positions in gene regulatory networks across plant species.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.2010.04459.x

Evolutionary and comparative analysis of MYB and bHLH plant transcription factors

Plant nutrition for sustainable development and global health

Regulation of gene expression at the level of transcription controls many crucial biological processes. Transcription factors (TFs) play a great role in controlling cellular processes and MYB TF family is large and involved in controlling various processes like responses to biotic and abiotic stresses, development, differentiation, metabolism, defense etc. Here, we review MYB TFs with particular emphasis on their role in controlling different biological processes. This will provide valuable insights in understanding regulatory networks and associated functions to develop strategies for crop improvement.

/pdf/myb-transcription-factor-genes-as-regulators-for-plant-1xuf8cbdfx.pdf

MYB transcription factor genes as regulators for plant responses: an overview

Petals of animal-pollinated angiosperms have adapted to attract pollinators. Factors influencing pollinator attention include colour and overall size of flowers. Colour is determined by the nature of the pigments, their environment and by the morphology of the petal epidermal cells. Most angiosperms have conical epidermal cells, which enhance the colour intensity and brightness of petal surfaces. The MYB-related transcription factor MIXTA controls the development of conical epidermal cells in petals of Antirrhinum majus. Another gene encoding an R2R3 MYB factor very closely related to MIXTA, AmMYBML2, is also expressed in flowers of A. majus. We have analysed the roles of AmMYBML2 and two MIXTA-related genes, PhMYB1 from Petunia hybrida and AtMYB16 from Arabidopsis thaliana, in petal development. The structural similarity between these genes, their comparable expression patterns and the similarity of the phenotypes they induce when ectopically expressed in tobacco, suggest they share homologous functions closely related to, but distinct from, that of MIXTA. Detailed phenotypic analysis of a phmyb1 mutant confirmed the role of PhMYB1 in the control of cell morphogenesis in the petal epidermis. The phmyb1 mutant showed that epidermal cell shape affects petal presentation, a phenotypic trait also observed following re-examination of mixta mutants. This suggests that the activity of MIXTA-like genes also contributes to petal form, another important factor influencing pollinator attraction.

/pdf/control-of-cell-and-petal-morphogenesis-by-r2r3-myb-22gn3vqos2.pdf

Control of cell and petal morphogenesis by R2R3 MYB transcription factors.

Shaping in plant cells.

The epidermal cells of petals of many species are specialized, having a pronounced conical shape. A transcription factor, MIXTA, is required for the formation of conical cells in Antirrhinum majus; in shoot epidermal cells of several species, expression of this gene is necessary and sufficient to promote conical cell formation. Ectopic expression has also shown MIXTA to be able to promote the formation of multicellular trichomes, indicating that conical cells and multicellular trichomes share elements of a common developmental pathway. Formation of conical cells or trichomes is also mutually exclusive with stomatal formation. In Antirrhinum, MIXTA normally only promotes conical cell formation on the inner epidermal layer of the petals. Its restricted action in cell fate determination results from its specific expression pattern. Expression of MIXTA, in turn, requires the activity of B-function genes, and biochemical evidence suggests that the products of DEFICIENS, GLOBOSA and SEPALLATA-related genes directly activate MIXTA expression late in petal development, after the completion of cell division in the petal epidermis. A MIXTA-like gene, AmMYBML1, is also expressed in petals. AmMYBML1 expression is high early in petal development. This gene may direct the formation of trichomes in petals. In specifying the fates of different cell types in petals, regulatory genes like MIXTA may have been duplicated. Changes in the timing and spatial localization of expression then provides similar regulatory genes which specify different cell fates.

/pdf/the-mechanics-of-cell-fate-determination-in-petals-1zepoujr5i.pdf

The mechanics of cell fate determination in petals.

Mechanotransduction: Kindlin' the fate of mesenchymal stem cells

Phase separation in stress resistance

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