Clade I TGACG-Motif Binding Basic Leucine Zipper Transcription Factors Mediate BLADE-ON-PETIOLE-Dependent Regulation of Development

Abstract

ORCID IDs: 0000-0001-9461-4369 (M.K.); 0000-0001-7587-4392 (M.B.); 0000-0002-6496-3792 (S.R.H.).Lateral organs formed by the shoot apical meristem (SAM) are separated from surrounding stem cells by regions of low growth called boundaries. Arabidopsis (Arabidopsis thaliana) BLADE-ON-PETIOLE1 (BOP1) and BOP2 represent a class of genes important for boundary patterning in land plants. Members of this family lack a DNA-binding domain and interact with TGACG-motif binding (TGA) basic Leu zipper (bZIP) transcription factors for recruitment to DNA. Here, we show that clade I bZIP transcription factors TGA1 and TGA4, previously associated with plant defense, are essential cofactors in BOP-dependent regulation of development. TGA1 and TGA4 are expressed at organ boundaries and function in the same genetic pathways as BOP1 and BOP2 required for SAM maintenance, flowering, and inflorescence architecture. Further, we show that clade I TGAs interact constitutively with BOP1 and BOP2, contributing to activation of ARABIDOPSIS THALIANA HOMEOBOX GENE1, which is needed for boundary establishment. These studies expand the functional repertoire of clade I TGA factors in development and defense.

Redox-active cysteines in TGACG-BINDING FACTOR 1 (TGA1) do not play a role in salicylic acid- or pathogen-induced expression of TGA1-regulated target genes inArabidopsis thaliana

“…However, the pentamer TGAC/G is sufficient for binding. Moreover, at least TGA1 binds to the A-box (TAC/GTA) in vivo (Wang et al , 2019) and tobacco TGA1a binds to A- and G- (CAC/GTG) boxes in vitro (Izawa et al , 1993). Therefore, we tested whether any of these potential binding sites is specifically enriched in promoters that are either lower or higher expressed in sid2 tga1 tga4 as compared to sid2 .…”

“…It is likely that this number would be even lower in the wild-type background since we observed more fluctuations in the presence of endogenous amounts of SA. The low frequency might be due to the expression pattern of TGA1/TGA4, the promoters of which are mainly active in the vascular tissue (Song et al , 2008; Wang et al , 2019). This correlates well with the expression pattern of the two robustly regulated target genes: DLO1 is expressed near the vascular tissue in Hpa -infected leaves (Zeilmaker et al , 2015), while BGL2 is expressed near the vascular tissue in SA-treated leaves (Spoel et al , 2009).…”

A Previously Undiscovered Role for Clade III TGA Basic Leucine Zipper Transcription Factors in BLADE-ON-PETIOLE Dependent Regulation of Plant Development

“…Loss-of-function bop1 bop2 mutations disrupt boundaries resulting in fused organs and changes in growth at the base of leaves and flowers that alter morphology and prevent abscission whereas up-regulation of BOP1 or BOP2 inhibits growth (Hepworth et al, 2005;McKim et al, 2008). BTB-ankyrin proteins like BOP1 and BOP2 have a transcriptional activation domain but no DNA-binding domain and interact with TGACG-motif binding (TGA) basic leucine zipper (bZIP) transcription factors for recruitment to DNA (reviewed in Khan et al, 2014;Wang et al, 2019). My thesis identifies a previously undiscovered role for clade III TGA factors (TGA3 and TGA7) in BOP-dependent regulation of plant development.…”

“…The BTB/POZ domain is required for the formation of dimers/heterodimers between family members and recruits E3 ubiquitin ligases to target proteins for degradation (Mukhtar et al, 2009;Spoel et al, 2009;Jun et al, 2010;Zhang et al, 2017;Chahtane et al, 2018). The ankyrin domain interacts with TGA bZIP proteins for recruitment to DNA (Zhang et al, 1999;Després et al, 2000;Zhou et al, 2000;Hepworth et al, 2005;Wang et al, 2019).…”

“…NPR1 is a master regulator of the salicylic acid (SA) mediated systemic acquired resistance (SAR) plant defense pathway (Cao et al, 1994;Cao et al, 1997). The other clade is comprised of BOP1 and BOP2, which control plant development and have a recently discovered role in innate immunity that is distinct from NPR1 (Ha et al, 2003;Hepworth et al, 2005;Norberg et al, 2005;Bergin, 2018;Wang et al, 2019; Figure 1.4B).…”