TheSEPALLATA MADS‐box proteinSLMBP21 forms protein complexes withJOINTLESSandMACROCALYXas a transcription activator for development of the tomato flower abscission zone

Abstract

SUMMARYOrgan abscission is a key step in a plant's life cycle and is one of the most important agronomic traits for crops. In tomato, two MADS-box genes, JOINTLESS (J) and MACROCAYLYX (MC), have been shown to be implicated in development of the flower abscission zone (AZ), but the molecular mechanisms underlying this process are not well known. We report here that the SEPALLATA (SEP) MADS-box gene SLMBP21 acts as an additional factor for development of the AZ in tomato. We show that knockdown of SLMBP21 abolishes development of the flower AZ, while overexpression of SLMBP21 produces small cells at the proximal section of the pedicel and the peduncle. Bimolecular fluorescence complementation analysis confirms that SLMBP21 interacts with J and MC, and co-immunoprecipitation assays further demonstrates that these three proteins may form higher-order protein complexes. In situ hybridization shows that SLMBP21, J, and MC transcripts accumulate in distinct regions, but overlap at the AZ vasculature. In addition, transactivation assays in yeast show that, of the three interacting proteins, only SLMBP21 can activate reporter gene transcription. RNA-seq analysis furthermore reveals that loss of function of SLMBP21, J, or MC affects a common subset of meristem activity genes including LeWUS and LATERAL SUPPRESSOR that were specifically expressed in the AZ on the tomato flower pedicel. Since SLMBP21 belongs to the FBP9/23 subclade of the SEP gene family, which is absent in Arabidopsis, the SLMBP21-J-MC complex may represent a distinct mechanism for development of the AZ in plants.

Genetic interactions of the unfinished flower development (ufd) mutant support a significant role of the tomato UFD gene in regulating floral organogenesis

“…Thereby, UFD could promote the expression of the different floral organ identity genes in the respective organ primordia allowing a normal flower development. In agreement, FA and MC are expressed in the FM and floral organ primordia, but they are not strongly expressed later during flower development (Molinero-Rosales et al 1999;Liu et al 2014;Yuste-Lisbona et al 2016).…”

MADS-domain transcription factors and the floral quartet model of flower development: linking plant development and evolution

“…Several MIKC-type genes have also been implicated in fruit development, and it is reasonable to assume that FQCs also play a role in this context. For example, FQCs are involved in the development of the fleshy fruits of tomato (Solanum lycopersicum); such proposed FQCs were shown to contain MIKC-type proteins, such as the StMADS11-like protein JOINTLESS, that are part of clades not belonging to those containing floral homeotic proteins (Liu et al, 2014;Fujisawa et al, 2014). Smaczniak et al (2012b) also identified complexes of several other MIKC-type proteins, in line with the hypothesis that they too are involved in protein tetramerization and FQC formation.…”

Transcriptome Profiling of Wheat Inflorescence Development from Spikelet Initiation to Floral Patterning Identified Stage-Specific Regulatory Genes

“…This is especially true for genes that are involved in meristem maintenance such as the CLV1 homologs (e.g. Traes_4AS_04E4A0063) that are highly expressed throughout the stages containing meristematic/primordial tissues, indicating that major functions of these key genes are conserved across the plant kingdom (Clark et al, 1997;Suzaki et al, 2004;Kobayashi et al, 2012;Liu et al, 2014b).…”