TAP Subfamily: LOB2

Conserved in a variety of evolutionarily divergent plant species, LOB DOMAIN (LBD) genes define a large, plant-specific family of largely unknown function. LBD genes have been implicated in a variety of developmental processes in plants, although to date, relatively few members have been assigned functions. LBD proteins have previously been predicted to be transcription factors, however supporting evidence has only been circumstantial. To address the biochemical function of LBD proteins, we identified a 6-bp consensus motif recognized by a wide cross-section of LBD proteins, and showed that LATERAL ORGAN BOUNDARIES (LOB), the founding member of the family, is a transcriptional activator in yeast. Thus, the LBD genes encode a novel class of DNA-binding transcription factors. Post-translational regulation of transcription factors is often crucial for control of gene expression. In our study, we demonstrate that members of the basic helix-loop-helix (bHLH) family of transcription factors are capable of interacting with LOB. The expression patterns of bHLH048 and LOB overlap at lateral organ boundaries. Interestingly, the interaction of bHLH048 with LOB results in reduced affinity of LOB for the consensus DNA motif. Thus, our studies suggest that bHLH048 post-translationally regulates the function of LOB at lateral organ boundaries (Husbands et al., 2007). According to (Huang et al., 2020) and (Zhang et al., 2020) the LBD family members can be classified into two subfamilies, namely class I and class II LBD proteins. These two classes are distinguished in their domain motifs. Compared to class I proteins, class II proteins lack an intact leucine-zipper-like domain (Zhang et al., 2020). In addition, zinc-finger motifs and GAS (Gly-Ala-Ser) blocks are present in both classes (Zhang et al., 2020).

References:

Husbands, A; Bell, EM; Shuai, B; Smith, HM; Springer, PS. 2007. LATERAL ORGAN BOUNDARIES defines a new family of DNA-binding transcription factors and can interact with specific bHLH proteins. Nucleic Acids Res. 35(19):6663-71

Lang, D; Weiche, B; Timmerhaus, G; Richardt, S; Riano-Pachon, DM; Correa, LG; Reski, R; Mueller-Roeber, B; Rensing, SA. 2010. Genome-wide phylogenetic comparative analysis of plant transcriptional regulation: a timeline of loss, gain, expansion, and correlation with complexity. Genome Biol Evol. 2: 488-503"

Huang, X., Yan, H., Liu, Y., & Yi, Y. (2020). Genome-wide analysis of LATERAL ORGAN BOUNDARIES DOMAIN-in Physcomitrella patens and stress responses. Genes & Genomics, 42(6), 651–662. https://doi.org/10.1007/s13258-020-00931-x

Zhang, Y., Li, Z., Ma, B., Hou, Q., & Wan, X. (2020). Phylogeny and Functions of LOB Domain Proteins in Plants. International Journal of Molecular Sciences, 21(7), 2278. https://doi.org/10.3390/ijms21072278