At-MINI ZINC FINGER2 and Sl-INHIBITOR OF MERISTEM ACTIVITY, a Conserved Missing Link in the Regulation of Floral Meristem Termination in Arabidopsis and Tomato

Abstract

In angiosperms, the gynoecium is the last structure to develop within the flower due to the determinate fate of floral meristem (FM) stem cells. The maintenance of stem cell activity before its arrest at the stage called FM termination affects the number of carpels that develop. The necessary inhibition at this stage of (), which is responsible for stem cell maintenance, involves a two-step mechanism. Direct repression mediated by the MADS domain transcription factor AGAMOUS (AG), followed by indirect repression requiring the C2H2 zinc-finger protein KNUCKLES (KNU), allow for the complete termination of floral stem cell activity. Here, we show that MINI ZINC FINGER2 (AtMIF2) and its homolog in tomato (), INHIBITOR OF MERISTEM ACTIVITY (SlIMA), participate in the FM termination process by functioning as adaptor proteins. AtMIF2 and SlIMA recruit AtKNU and SlKNU, respectively, to form a transcriptional repressor complex together with TOPLESS and HISTONE DEACETYLASE19. AtMIF2 and SlIMA bind to the and loci in the respective plants, leading to their repression. These results provide important insights into the molecular mechanisms governing (FM) termination and highlight the essential role of AtMIF2/SlIMA during this developmental step, which determines carpel number and therefore fruit size.

The flowering hormone florigen accelerates secondary cell wall biogenesis to harmonize vascular maturation with reproductive development

“…If MIFs are required for the normal course of SCWB in stems as legitimate components of the florigen-SCWB developmental program, then their overexpression would be expected to enhance it. Indeed, 35S:TMIF2-FLAG and 35S:TMIF3 plants, in addition to the already reported growth retardation and fruit development (40,43), feature rigid slender stems with an extensive, precociously lignified secondary xylem ( Fig. 5 J and L) but a normal flowering time.…”

“…5F). In tomato, the MIF genes are expressed at moderate levels in all organs, and their 5 regulatory regions contain potential MADS-responsive elements (40,43). We could not find a severe defect in mif2 cr1 stems, but plants with mif3 cr1 single or mif2 cr1 mif3 cr1 double mutants (SI Appendix, Figs.…”

“…To test this assumption, we used CRISPR-editing (39) to mutate several genes that are modified in stems. Here we focused on 2 MIF genes, MINI ZINC FINGERS (40)(41)(42)(43), which are activated by SFT and TFUL2 but, conversely, silenced in GinFT stems (Fig. 5F).…”

Mitotic Inheritance of PRC2-Mediated Silencing: Mechanistic Insights and Developmental Perspectives

“…This coupling fine-tunes the number of floral organs produced by the meristem and thus conditions the reproductive fitness of the plant. Interestingly, this mechanism might be conserved in other dicots such as tomato (Bollier et al, 2018) and monocots such as the rice (Conrad et al, 2014).…”

Induced ovule-to-flower switch by interfering with SlIMA activity in tomato

“…First, AG directly represses WUS during the early stages of FM termination, 2 and next AG acts indirectly through the parallel activation of the expression of two genes, encoding a transcription factor belonging to the C 2 H 2 zinc-finger protein family named KNUCKLES (KNU), 3,4 and a MINI ZINC FINGER protein named MIF2. 5 To ensure the complete repression of WUS, MIF2 recruits KNU to form a transcriptional repressor complex, together with TOPLESS (TPL) and HISTONE DEACETYLASE19 (HDA19), which binds to the WUS locus leading to its complete repression. We recently demonstrated the conservation of this AG-KNU-MIF2-WUS pathway between Arabidopsis and tomato.…”