The first MYB gene identified was the "oncogene" v-Myb derived from the avian myeloblastosis virus and later the corresponding human cellular homolog c-Myb was identified.  Classical MYB factors, which are related to c-Myb, seem to be involved in the control of the cell cycle in animals, plants and other higher eukaryotes.

MYB factors represent a very large and diverse gene family where proteins with two MYB repeats (R2R3, each approximately 50 aa long) are the most common ones, but proteins with just one repeat or three or four repeats are found, too. Each motif consists of three alpha-helices, where the second and third form a helix-turn-helix structure, and the third helix is thought to make contact with the major groove of DNA. Three tryptophan residues in each repeat, spaced by 18-21 aa, form a very conserved cluster among all MYB factors. Compared to the highly conserved MYB domain, other regions in MYB proteins can be highly variable.

Today, more than 200 MYB factors are identified in maize (Zea mays) and rice (Oryza sativa) and a comparably high number in other related monocots. Structurally and functionally very diverse MYB factors can be involved in the control of mainly plant specific processes such as plant secondary metabolism, cell morphogenesis or cell fate (Wu et al., 2022).

The first plant MYB gene C1 (ZmMYB1) was isolated from maize, which encodes a c-MYB-like transcription factor.  C1 regulates the Bz1 and A1 structural genes involved in anthocyanin biosynthesis by (Paz-Ares et al., 1986, Cone et al., 1986, Paz-Ares et al., 1987, Martin et al., 1997). C1 was found to depend on the basic helix-loop-helix (bHLH) proteins R (ZmbHLH1) or B (ZmbHLH2) for regulatory function, whereas the closely related Myb protein P1 (ZmMYB3) does not (Grotewold et al., 2000, Dias et al., 2003). Interestingly, P1 is also highly expressed in leaves of maize landraces adapted to high altitudes and higher levels of UV-B radiation. Epigenetic regulation is involved as supported by the observation that ​​DNA methylation in the P1 proximal promoter, intron1 and intron2 is decreased by UV-B in all high altitude lines analyzed (Rius et al., 2016, Li et al., 2022). It has been recognized that MYB factors play a prominent role in regulation of anthocyanin biosynthesis and secondary metabolism in all plant species (Cao et al., 2020, Yan et al., 2021).

The MYB-CC gene family encode proteins that harbor a combination of characteristic myeloblastosis (MYB) and coiled-coil (CC) domain structures. Some MYB-CC genes have been demonstrated to represent transcription factors regulating phosphate uptake and controlling the starvation response in plants. A total of 12 maize MYB-CC genes (ZmMYB-CC1 to ZmMYB-CC12) were identified located in six out of the 10 chromosomes of maize (Bai et al., 2019).

Last updated June 2023 by John Gray

References:

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