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SUMMARY: Phytoplasmas are pathogenic bacteria that reprogram plant host development for their own benefit. Previous studies have characterized a few different phytoplasma effector proteins that destabilize specific plant transcription factors. However, these are only a small fraction of the potential effectors used by phytoplasmas; therefore, the molecular mechanisms through which phytoplasmas modulate their hosts require further investigation. To obtain further insights into the phytoplasma infection mechanisms, we generated a protein–protein interaction network between a broad set of phytoplasma effectors and a large, unbiased collection of Arabidopsis thaliana transcription factors and transcriptional regulators. We found widespread, but specific, interactions between phytoplasma effectors and host transcription factors, especially those related to host developmental processes. In particular, many unrelated effectors target specific sets of TCP transcription factors, which regulate plant development and immunity. Comparison with other host‐pathogen protein interaction networks shows that phytoplasma effectors have unusual targets, indicating that phytoplasmas have evolved a unique and unusual infection strategy. This study contributes a rich and solid data source that guides further investigations of the functions of individual effectors, as demonstrated for some herein. Moreover, the dataset provides insights into the underlying molecular mechanisms of phytoplasma infection. Significance Statement: This work shows that the effectors of phytoplasma, a globally economically important bacterial plant pathogen, have pervasive interactions with development‐related host transcription factors, providing a way to take over plant growth and development in favor of the pathogen and its insect vector. The obtained comprehensive protein interaction network and a showcase of the potential biological consequences of a selected effector advance our understanding of phytoplasma‐host interactions and provide guidance for further study. [ABSTRACT FROM AUTHOR]

The Asteraceae is the largest angiosperm family with more than 25,000 species. Individual studies have shown that MADS-box and TCP transcription factors are regulators of the development and symmetry of flowers, contributing to their iconic flower-head (capitulum) and floret. However, a systematic study of MADSbox and TCP genes across the Asteraceae is lacking. We performed a comparative analysis of genome sequences of 33 angiosperm species including our de novo assembly of diploid sexual dandelion (Taraxacum officinale) and 11 other Asteraceae to investigate the lineage-specific evolution of MADS-box and TCP genes in the Asteraceae. We compared the phylogenomic results of MADS-box and TCP genes with their expression in T. officinale floral tissues at different developmental stages to demonstrate the regulation of genes with Asteraceae-specific attributes. Here, we show that MADS-box MIKCc and TCP-CYCLOIDEA (CYC) genes have expanded in the Asteraceae. The phylogenomic analysis identified AGAMOUS-like (AG-like: SEEDSTICK [STK]-like), SEPALATA-like (SEP3-like), and TCP-PROLIFERATING CELL FACTOR (PCF)-like copies with lineage-specific genomic contexts in the Asteraceae, Cichorioideae, or dandelion. Different expression patterns of some of these gene copies suggest functional divergence. We also confirm the presence and revisit the evolutionary history of previously named "Asteraceae-Specific MADSbox genes (AS-MADS)." Specifically, we identify non-Asteraceae homologs, indicating a more ancient origin of this gene clade. Syntenic relationships support that AS-MADS is paralogous to FLOWERING LOCUS C (FLC) as demonstrated by the shared ancient duplication of FLC and SEP3. [ABSTRACT FROM AUTHOR]

Over the last decade, the yeast two-hybrid system has become the tool to use for the identification of protein-protein interactions and recently, even complete interactomes were elucidated by this method. Nevertheless, it is an artificial system that is sensitive to errors resulting in the identification of false-positive and false-negative interactions. In this study, plant MADS box transcription factor interactions identified by yeast two-hybrid systems where studied in living plant cells by a technique based on fluorescence resonance energy transfer (FRET). Petunia MADS box proteins were fused to either cyan fluorescent protein or yellow fluorescent protein and transiently expressed in protoplasts followed by FRET-spectral imaging microscopy and FRET-fluorescence lifetime imaging microscopy to detect FRET and hence protein-protein interactions. All petunia MADS box heterodimers identified in yeast were confirmed in protoplasts. However, in contrast to the yeast two-hybrid results, homodimerization was demonstrated in plant cells for three petunia MADS box proteins. Heterodimers were identified between the ovule-specific MADS box protein FLORAL BINDING PROTEIN 11 and members of the petunia FLORAL BINDING PROTEIN 2 subfamily, which are also expressed in ovules, suggesting that these dimers play a role in ovule development. Furthermore, the role of dimerization in translocation of MADS box protein dimers to the nucleus is demonstrated, and the nuclear localization signal of MADS box proteins has been mapped to the N-terminal region of the MADS domain by means of mutant analyses.

Tomato is one of the most cultivated vegetables in the world and an important ingredient of the human diet. Tomato breeders and growers face a continuous challenge of combining high quantity (production volume) with high quality (appearance, taste and perception for the consumers, processing quality for the processing industry). To improve the quality of tomato, it is important to understand the regulation of fruit development and of fruit cellular structure, which is in part determined by the sizes and numbers of cells within a tissue. The role of the cell cycle therein is poorly understood. Plant cyclin-dependent kinases ( CDKs) are homologues of yeast cdc2, an important cell cycle regulator conserved throughout all eukaryotes. CDKA1 is constitutively expressed during the cell cycle and has dual functions in S- and M-phase progression. We have produced transgenic tomato plants with increased expression of CDKA1 under the control of the fruit-specific TPRP promoter, which despite a reduced number of seeds and diminished amount of jelly, developed fruits with weight and shape comparable to that of wild-type fruits. However, the phenotypic changes with regard to the pericarp thickness and placenta area were remarkable. Fruits of tomato plants with the highest expression of CDKA1 had larger septa and columella (placenta), compared with wild-type fruits. Our data demonstrate the possibility of manipulating the ratio between cell division and expansion by changing the expression of a key cell cycle regulator and probably its activity with substantial effects on structural traits of the harvested fruit. [ABSTRACT FROM AUTHOR]

MADS-domain transcription factors are essential for proper flower and seed development in angiosperms and their role in determination of floral organ identity can be described by the ‘ABC model’ of flower development. Recently, close relatives of the B-type genes were identified by phylogenetic studies, which are referred to as Bsister (Bs) genes. Here, we report the isolation and characterization of a MADS-box Bs member from petunia, designated FBP24. An fbp24 knock-down line appeared to closely resemble the Arabidopsis Bs mutant abs and a detailed and comparative analysis led to the conclusion that both FBP24 and ABS are necessary to determine the identity of the endothelial layer within the ovule. Protein interaction studies revealed the formation of higher-order complexes between Bs–C–E and Bs–D–E type MADS-box proteins, suggesting involvement of these specific complexes in determination of endothelium identity. However, although there are many similarities between the two genes and their products and functions, interestingly FBP24 cannot replace ABS in Arabidopsis. The results presented here demonstrate the importance of the comparative analysis of key regulatory genes in various model systems to fully understand all aspects of plant development. [ABSTRACT FROM AUTHOR]

Examines the molecular regulation of nectary development. Use of reverse transcriptase-polymerase chain reaction in cloning of NEC1, a gene expressed in the nectaries of Petunia hybrida; Presence of NEC1 protein in the nectaries; Role of NEC1 gene in sugar metabolism and nectar secretion.