PaMYB82 from Platanus acerifolia regulates trichome development in transgenic Arabidopsis

Functional identification of AaMYB113 and AaMYB114 from Aeonium arboreum 'Halloween' in model plants

Aeonium arboreum 'Halloween', a popular indoor ornamental succulent in China, changes its leaf colour to red on light exposure. However, the underlying molecular mechanisms is still vague. Comparative analysis of transcriptome data from 'Halloween' leaves treated under dark and light conditions revealed two R2R3-MYB transcription factors, AaMYB113 and AaMYB114, that may mediate anthocyanin accumulation. In this study, we cloned the AaMYB113 and AaMYB114 genes, encoding proteins of 279 and 248 amino acids, respectively. Transcriptional activity analysis revealed that AaMYB113 exhibits strong transcriptional activity, in contrast to AaMYB114, which demonstrates minimal activity. Transient expression studies in tobacco leaves demonstrated that AaMYB113 induced red pigmentation, whereas AaMYB114 did not. Subsequent stable overexpression in Arabidopsis thaliana confirmed that AaMYB113, but not AaMYB114, could similarly turn Arabidopsis leaves red. Further stable transformation of AaMYB113 in tobacco affected multiple floral components, including leaves, petals, calyx, flower tubes, and filaments, turning them red. Quantitative real-time PCR (qRT-PCR) assay in leaves of AaMYB113 stably transformed tobacco and Arabidopsis revealed upregulation of anthocyanin biosynthesis-related structural genes and TT8-like transcription factors. Moreover, the dual luciferase analysis confirmed that AaMYB113 can activate the promoters of 'Halloween' anthocyanin synthesis structural genes, AaCHS, AaCHI, AaF3H, AaDFR and AaANS. The above results indicate that AaMYB113 can promote anthocyanin synthesis, while AaMYB114 does not have this function. This study contributes significantly to the limited body of research on the molecular mechanisms of anthocyanin synthesis in succulents, advancing our understanding of how these pathways are regulated in 'Halloween' succulents and potentially other species.

Genome-wide identification of bHLH transcription factors and functional analysis in salt gland development of the recretohalophyte sea lavender (Limonium bicolor)

Transcription factors with basic helix-loop-helix (bHLH) structures regulate plant growth, epidermal structure development, metabolic processes, and responses to stress extensively. Sea lavender (Limonium bicolor) is a recretohalophyte with unique salt glands in the epidermis that make it highly resistant to salt stress, contributing to the improvement of saline lands. However, the features of the bHLH transcription factor family in L. bicolor are largely unknown. Here, we systematically analyzed the characteristics, localization, and phylogenetic relationships of 187 identified bHLH family genes throughout the L. bicolor genome, as well as their cis-regulatory promoter elements, expression patterns, and key roles in salt gland development or salt tolerance by genetic analysis. Nine verified L. bicolor bHLH genes are expressed and the encoded proteins function in the nucleus, among which the proteins encoded by Lb2G14060 and Lb1G07934 also localize to salt glands. Analysis of CRISPR-Cas9-generated knockout mutants and overexpression lines indicated that the protein encoded by Lb1G07934 is involved in the formation of salt glands, salt secretion, and salt resistance, indicating that bHLH genes strongly influence epidermal structure development and stress responses. The current study lays the foundation for further investigation of the effects and functional mechanisms of bHLH genes in L. bicolor and paves the way for selecting salt-tolerance genes that will enhance salt resistance in crops and for the improvement of saline soils.

The Abundant and Unique Transcripts and Alternative Splicing of the Artificially Autododecaploid London Plane (Platanus × acerifolia)

Transcription and alternative splicing (AS) are now appreciated in plants, but few studies have examined the effects of changing ploidy on transcription and AS. In this study, we showed that artificially autododecaploid plants of London plane (Platanus × acerifolia (Aiton) Willd) had few flowers relative to their hexaploid progenitors. Transcriptome analysis based on full-length Oxford Nanopore Technologies (ONTs) and next-generation sequencing (NGS) revealed that the increased ploidy level in P. × acerifolia led to more transcribed isoforms, accompanied by an increase in the number of isoforms per gene. The functional enrichment of genes indicated that novel genes transcribed specifically in the dodecaploids may have been highly correlated with the ability to maintain genome stability. The dodecaploids showed a higher number of genes with upregulated differentially expressed genes (DEGs) compared with the hexaploid counterpart. The genome duplication of P. × acerifolia resulted mainly in the DEGs involved in basic biological pathways. It was noted that there was a greater abundance of alternative splicing (AS) events and AS genes in the dodecaploids compared with the hexaploids in P. × acerifolia. In addition, a significant difference between the structure and expression of AS events between the hexaploids and dodecaploids of Platanus was found. Of note, some DEGs and differentially spliced genes (DSGs) related to floral transition and flower development were consistent with the few flower traits in the dodecaploids of P. × acerifolia. Collectively, our findings explored the difference in transcription and AS regulation between the hexaploids and dodecaploids of P. × acerifolia and gained new insight into the molecular mechanisms underlying the few-flower phenotype of P. × acerifolia. These results contribute to uncovering the regulatory role of transcription and AS in polyploids and breeding few-flower germplasms.

Evolution and functional diversification of R2R3-MYB transcription factors in plants

R2R3-MYB genes (R2R3-MYBs) form one of the largest transcription factor gene families in the plant kingdom, with substantial structural and functional diversity. However, the evolutionary processes leading to this amazing functional diversity have not yet been clearly established. Recently developed genomic and classical molecular technologies have provided detailed insights into the evolutionary relationships and functions of plant R2R3-MYBs. Here, we review recent genome-level and functional analyses of plant R2R3-MYBs, with an emphasis on their evolution and functional diversification. In land plants, this gene family underwent a large expansion by whole genome duplications and small-scale duplications. Along with this population explosion, a series of functionally conserved or lineage-specific subfamilies/groups arose with roles in three major plant-specific biological processes: development and cell differentiation, specialized metabolism, and biotic and abiotic stresses. The rapid expansion and functional diversification of plant R2R3-MYBs are highly consistent with the increasing complexity of angiosperms. In particular, recently derived R2R3-MYBs with three highly homologous intron patterns (a, b, and c) are disproportionately related to specialized metabolism and have become the predominant subfamilies in land plant genomes. The evolution of plant R2R3-MYBs is an active area of research, and further studies are expected to improve our understanding of the evolution and functional diversification of this gene family.

Advances in the Regulation of Epidermal Cell Development by C2H2 Zinc Finger Proteins in Plants

Plant epidermal cells, such as trichomes, root hairs, salt glands, and stomata, play pivotal roles in the growth, development, and environmental adaptation of terrestrial plants. Cell fate determination, differentiation, and the formation of epidermal structures represent basic developmental processes in multicellular organisms. Increasing evidence indicates that C2H2 zinc finger proteins play important roles in regulating the development of epidermal structures in plants and plant adaptation to unfavorable environments. Here, we systematically summarize the molecular mechanism underlying the roles of C2H2 zinc finger proteins in controlling epidermal cell formation in plants, with an emphasis on trichomes, root hairs, and salt glands and their roles in plant adaptation to environmental stress. In addition, we discuss the possible roles of homologous C2H2 zinc finger proteins in trichome development in non-halophytes and salt gland development in halophytes based on bioinformatic analysis. This review provides a foundation for further study of epidermal cell development and abiotic stress responses in plants.

Expression of the subgroup IIIf bHLH transcription factor CpbHLH1 from Chimonanthus praecox (L.) in transgenic model plants inhibits anthocyanin accumulation

KEY MESSAGE

Overexpression of CpbHLH1 in Arabidopsis and tobacco resulted in a dramatic decrease in anthocyanin accumulation by repressing the expression of late biosynthesis genes in the flavonoid biosynthesis pathway. Many basic helix-loop-helix (bHLH) transcription factors (TFs) of subgroup IIIf have been characterized as anthocyanin-associated activators in higher plants, but information regarding bHLH TFs that inhibit anthocyanin accumulation remains scarce. In this study, the subgroup IIIf bHLH TF CpbHLH1 from Chimonanthus praecox (L.) was identified as a negative regulator of anthocyanin accumulation. Our results showed that overexpression of CpbHLH1 in model plant species, Arabidopsis and tobacco, resulted in a dramatic decrease in anthocyanin content, whereas the content of proanthocyanidin was little affected. Quantitative RT-PCR (qRT-PCR) assays of the structural genes in the flavonoid biosynthesis pathway revealed that CpbHLH1 inhibits anthocyanin accumulation mainly through repressing the expression of late biosynthesis genes (LBGs). Interactions between CpbHLH1 protein and AtPAP1/NtAN2 protein were detected via yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. This is the first bHLH repressor of anthocyanin biosynthesis identified in dicotyledons. These results can help us better understand the anthocyanin regulatory network in plants and may provide insights into the diverse functions of bHLH proteins.