One of the first myb-like genes to be studied was AtMybL2 which was isolated from an Arabidopsis thaliana cDNA library (Dubos et al., 2008, Matsui et al., 2008). The AtMYL2 transcript was preferentially found in leaves. The predicted gene product posesses a conservative N terminal myb-domain known to be involved in DNA-binding and a unique proline-rich C-terminal part. The single myb-domain (R3-MYB)(PF00249) includes only one of the typical two or three tryptophan repeats found in other myb-like proteins.

The loss of MYBL2 activity in the seedlings of two independent T-DNA insertion mutants led to a dramatic increase in the accumulation of anthocyanin in Arabidopsis. In addition, overexpression of MYBL2 in seeds inhibited the biosynthesis of PAs (Dubos et al., 2008, Matsui et al., 2008) suggesting that AtMYBL2 has a repressive regulatory function.  Transient expression analysis in A. thaliana cells suggested that AtMYBL2 interacts with MYB-BHLH-WDR (MBW) complexes in planta and directly modulates the expression of flavonoid target genes. The minimal repression domain of AtMYBL2 was found to be the six amino acids (TLLLFR) at the carboxyl terminus, and TLLLFR appears to be a novel repression motif that is different from the ERF-associated amphiphilic repression (EAR) motif (Matsui et al., 2008). More recently it has been found that AtGLK1 acts upstream of MYBL2 to genetically regulate sucrose-induced anthocyanin biosynthesis in Arabidopsis (Zhao et al., 2021)

In maize at least 68 Myb-related (MYBR) genes have been identified. One of the first MYBR genes in maize to be identified was MRP1 (MYB Related Protein 1, ZmMYBR1). ZmMRP-1 is first expressed soon after fertilization, when the endosperm is still a multinuclear coenocyte. The transcript accumulates in the basal nucleocytoplasmic domain that gives rise to transfer cells after cellularization. The transcript can be detected throughout transfer cell development, but it is not found in mature cells. ZmMRP-1 strongly transactivates the promoters of two unrelated transfer cell-specific genes. The properties of ZmMRP-1 are consistent with it being a determinant of transfer cell-specific expression (Gómez et al., 2002).

Last updated June 2023 by John Gray

References:

Dubos C, Le Gourrierec J, Baudry A, Huep G, Lanet E, Debeaujon I, Routaboul JM, Alboresi A, Weisshaar B, Lepiniec L. MYBL2 is a new regulator of flavonoid biosynthesis in Arabidopsis thaliana. Plant J. 2008 Sep;55(6):940-53. doi: 10.1111/j.1365-313X.2008.03564.x. Epub 2008 Jun 4. PMID: 18532978.

Matsui K, Umemura Y, Ohme-Takagi M. AtMYBL2, a protein with a single MYB domain, acts as a negative regulator of anthocyanin biosynthesis in Arabidopsis. Plant J. 2008 Sep;55(6):954-67. doi: 10.1111/j.1365-313X.2008.03565.x. Epub 2008 Jun 4. PMID: 18532977.

Zhao D, Zheng Y, Yang L, Yao Z, Cheng J, Zhang F, Jiang H, Liu D. The transcription factor AtGLK1 acts upstream of MYBL2 to genetically regulate sucrose-induced anthocyanin biosynthesis in Arabidopsis. BMC Plant Biol. 2021 May 28;21(1):242. doi: 10.1186/s12870-021-03033-2. PMID: 34049482; PMCID: PMC8162001.

Gómez E, Royo J, Guo Y, Thompson R, Hueros G. Establishment of cereal endosperm expression domains: identification and properties of a maize transfer cell-specific transcription factor, ZmMRP-1. Plant Cell. 2002 Mar;14(3):599-610. doi: 10.1105/tpc.010365. PMID: 11910007; PMCID: PMC150582.