VERDANDIIs a Direct Target of the MADS Domain Ovule Identity Complex and Affects Embryo Sac Differentiation inArabidopsis 

Abstract

In Arabidopsis thaliana, the three MADS box genes SEEDSTICK (STK), SHATTERPROOF1 (SHP1), and SHP2 redundantly regulate ovule development. Protein interaction studies have shown that a multimeric complex composed of the ovule identity proteins together with the SEPALLATA MADS domain proteins is necessary to determine ovule identity. Despite the extensive knowledge that has become available about these MADS domain transcription factors, little is known regarding the genes that they regulate. Here, we show that STK, SHP1, and SHP2 redundantly regulate VERDANDI (VDD), a putative transcription factor that belongs to the plant-specific B3 superfamily. The vdd mutant shows defects during the fertilization process resulting in semisterility. Analysis of the vdd mutant female gametophytes indicates that antipodal and synergid cell identity and/or differentiation are affected. Our results provide insights into the pathways regulated by the ovule identity factors and the role of the downstream target gene VDD in female gametophyte development.

MADS Domain Transcription Factors Mediate Short-Range DNA Looping That Is Essential for Target Gene Expression in Arabidopsis

“…Especially CArG box 1 and 3 seem to be most important for the establishment of loop formation. This is in agreement with ChIP experiments that showed that in vivo STK and SEP3 only use CArG box 1 and 3 in the VDD promoter (Matias-Hernandez et al, 2010). Interestingly, when we tested by TPM assays the VDD promoter with a single CArG box deletion, loop formation was only observed when the CArG box 2 was deleted.…”

“…Furthermore, they regulate the expression of VDD through direct binding to its promoter region (Favaro et al, 2003;Matias-Hernandez et al, 2010). The VDD promoter region contains three CArG boxes within the region 1000 bp upstream of the ATG start codon ( Figure 1A; Matias-Hernandez et al, 2010). Cooperative binding of the tetramers (composed of two SEP3-STK heterodimers) to two of the three adjacent CArG boxes would induce the formation of loops within the promoter region, which might have important regulatory functions.…”

“…Furthermore, they regulate the expression of VDD through direct binding to its promoter region (Favaro et al, 2003;Matias-Hernandez et al, 2010). The VDD promoter region contains three CArG boxes within the region 1000 bp upstream of the ATG start codon ( Figure 1A; Matias-Hernandez et al, 2010).…”

“…Recently, we identified VERDANDI (VDD), a gene belonging to the REPRODUCTIVE MERISTEM family (Romanel et al, 2009), as a target of the ovule identity factors STK, SHP1, SHP2, and SEP3 (Matias-Hernandez et al, 2010). VDD transcripts are present in the same tissues as these ovule identity genes and silencing of the ovule identity genes, STK, SHP1, and SHP2, led to the complete absence of VDD expression during ovule development.…”

“…VDD transcripts are present in the same tissues as these ovule identity genes and silencing of the ovule identity genes, STK, SHP1, and SHP2, led to the complete absence of VDD expression during ovule development. Analysis of the VDD mutant revealed that this gene is important for female gametophyte cell identity determination (Matias-Hernandez et al, 2010).…”