Anthocyanins, a group of flavonoids, play diverse roles in plant growth and environmental adaptation. The biosynthesis and accumulation of anthocyanin are regulated by environmental cues, such as high light. However, the precise mechanism underlying anthocyanin biosynthesis under high light conditions remains largely unclear. Here, we report that the R3-MYB repressor MYB-LIKE 2 (MYBL2) negatively regulates high light-induced anthocyanin biosynthesis in Arabidopsis by repressing two R2R3-MYB activators, PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) and PAP2, which are core components of the MYB-bHLH-WD40 (MBW) complex. We found that MYBL2 interacts with PAP1/2 and reduces their transcriptional activation activities, thus disrupting the expression of key genes involved in anthocyanin biosynthesis, such as DIHYDROFLAVONOL 4-REDUCTASE (DFR) and TRANSPARENT TESTA 19 (TT19). Additionally, MYBL2 attenuates the transcriptional activation of PAP1 and its own expression, but not that of PAP2. Conversely, PAP1 collaborates with TRANSPARENT TESTA 8 (TT8), a bHLH member of the MBW complex, to activate MYBL2 transcription when excessive anthocyanins are accumulated. Taken together, our findings reveal a negative feedback regulatory module composed of MYBL2 and PAP1 that fine-tunes high light-induced anthocyanin biosynthesis through modulating MBW complex assembly.

Verticillium wilt (VW) caused by Verticillium dahliae (V. dahliae) is one of the most destructive diseases in cotton (Gossypium spp.). Histone acetylation plays critical roles in plant development and adaptive responses to biotic and abiotic stresses. However, the relevance of histone acetylation in cotton VW resistance remains largely unclear. Here, we identified histone deacetylase 5 (GhHDA5) from upland cotton (Gossypium hirsutum L.), as a negative regulator of VW resistance. GhHDA5 expression was responsive to V. dahliae infection. Silencing GhHDA5 in upland cotton led to improved resistance to V. dahliae, while heterologous expression of GhHDA5 in Arabidopsis (Arabidopsis thaliana) compromised V. dahliae tolerance. GhHDA5 repressed the expression of several lignin biosynthesis-related genes, such as 4-coumarate:CoA ligase gene Gh4CL3 and ferulate 5-hydroxylase gene GhF5H, through reducing the acetylation level of histone H3 lysine 9 and 14 (H3K9K14ac) at their promoter regions, thereby resulting in an increased deposition of lignin, especially S monomers, in the GhHDA5-silenced cotton plants. The silencing of GhF5H impaired cotton VW tolerance. Additionally, the silencing of GhHDA5 also promoted the production of reactive oxygen species (ROS), elevated the expression of several pathogenesis-related genes (PRs), and altered the content and signaling of the phytohormones salicylic acid (SA), jasmonic acid (JA), and strigolactones (SLs) after V. dahliae infection. Taken together, our findings suggest that GhHDA5 negatively regulates cotton VW resistance through modulating disease-induced lignification and the ROS- and phytohormone-mediated defense response.

In higher plants, COP1 (Constitutively Photomorphogenic 1) acts as a central regulator of light-signaling networks and globally conditions the target proteins via the ubiquitin-proteasome pathway. However, the function of COP1-interacting proteins in light-regulated fruit coloration and development remains unknown in Solanaceous plants. Here, a COP1-interacting protein-encoding gene, SmCIP7, expressed specifically in the eggplant (Solanum melongena L.) fruit, was isolated. Gene-specific silencing of SmCIP7 using RNA interference (RNAi) significantly altered fruit coloration, fruit size, flesh browning, and seed yield. SmCIP7-RNAi fruits showed evident repression of the accumulation of anthocyanins and chlorophyll, indicating functional similarities between SmCIP7 and AtCIP7. However, the reduced fruit size and seed yield indicated SmCIP7 had evolved a distinctly new function. With the comprehensive application of HPLC-MS, RNA-seq, qRT-PCR, Y2H, BiFC, LCI, and dual-luciferase reporter system (DLR™), it was found that SmCIP7, a COP1 interactive protein in light signaling promoted anthocyanin accumulation, probably by regulating the transcription of SmTT8. Additionally, the drastic up-regulation of SmYABBY1, a homologous gene of SlFAS, might account for the strongly retarded fruit growth in SmCIP7-RNAi eggplant. Altogether, this study proved that SmCIP7 is an essential regulatory gene to modulate fruit coloration and development, serving as a key gene locus in eggplant molecular breeding.

Background The evolutionarily conserved Polycomb Repressive Complex 2 (PRC2) plays a vital role in epigenetic gene repression by depositing tri-methylation on lysine residue K27 of histone H3 (H3K27me3) at the target loci, thus participating in diverse biological processes. However, few reports about PRC2 are available in plant species with large and complicated genomes, like cotton. Results Here, we performed a genome-wide identification and comprehensive analysis of cotton PRC2 core components, especially in upland cotton ( Gossypium hirsutum ). Firstly, a total of 8 and 16 PRC2 core components were identified in diploid and tetraploid cotton species, respectively. These components were classified into four groups, E(z), Su(z)12, ESC and p55, and the members in the same group displayed good collinearity, similar gene structure and domain organization. Next, we cloned G. hirsutum PRC2 (GhPRC2) core components, and found that most of GhPRC2 proteins were localized in the nucleus, and interacted with each other to form multi-subunit complexes. Moreover, we analyzed the expression profile of GhPRC2 genes. The transcriptome data and quantitative real-time PCR (qRT-PCR) assays indicated that GhPRC2 genes were ubiquitously but differentially expressed in various tissues, with high expression levels in reproductive organs like petals, stamens and pistils. And the expressions of several GhPRC2 genes, especially E(z) group genes, were responsive to various abiotic and biotic stresses, including drought, salinity, extreme temperature, and Verticillium dahliae ( Vd ) infection. Conclusion We identified PRC2 core components in upland cotton, and systematically investigated their classifications, phylogenetic and synteny relationships, gene structures, domain organizations, subcellular localizations, protein interactions, tissue-specific and stresses-responsive expression patterns. Our results will provide insights into the evolution and composition of cotton PRC2, and lay the foundation for further investigation of their biological functions and regulatory mechanisms.

As an oil crop with good taste and profuse nutrition, peanut ( Arachis hypogaea L.) is grown worldwide, mainly for edible seeds. Black peanuts attract more attention for their appealing color and health-promoting anthocyanins. Here, two cyanidin-based anthocyanins and four quercetin-based flavonols were separated and identified from skins of two black cultivars (Zi Yu and Zi Guan) by HPLC-ESI-Q-TOF-MS. To study the anthocyanin accumulation, libraries constructed from the mRNA of skins of Zi Yu and white cultivar (Bai Yu) were sequenced, and 4042 differentially expressed genes were identified. Gene ontology and KEGG pathway analysis underlined the importance of the high expression of flavonoid biosynthetic and regulatory genes in seed skin of Zi Yu. Furthermore, expression profiles of these genes were analyzed carefully in four representative peanut cultivars. Altogether, these results strongly indicate that the up-regulation of transcriptional activators (AhMYB1, AhMYB2, and AhTT8) accounts for the skin-specific accumulation of anthocyanins in black peanut.

Background Water scarcity is considered to be a severe environmental constraint to plant survival and productivity. Studies on drought-tolerant plants would definitely promote a better understanding of the regulatory mechanism lying behind the adaptive response of plants to drought. Opisthopappus taihangensis (ling) shih is a typical drought-tolerant perennial plant species endemically distributed across the Taihang Mountains in China, but the underlying mechanism for drought tolerance of this particular species remains elusive. Results To mimic natural drought stress, O. taihangensis plants were treated with two different concentrations (25% and 5%) of polyethylene glycol (PEG6000), which represent the H group (high salinity) and the L group (low salinity), respectively. The physiological characteristics of these two groups of plants, including relative water content maintenance (RWC), proline content and chlorophyll content were assessed and compared with plants in the control group (CK), which had normal irrigation. There was not a significant difference in RWC when comparing plants in the L group with the control group. Proline was accumulated to a higher level, and chlorophyll content was decreased slightly in plants under low drought stress. In plants from the H group, a lower RWC was observed. Proline was accumulated to an even higher level when compared with plants from the L group, and chlorophyll content was further reduced in plants under high drought stress. Transcriptomic analysis was carried out to look for genes that are differentially expressed (DEGs) in O. taihangensis plants coping adaptively with the two levels of drought stress. A total of 23,056 genes are differentially expressed between CK and L, among which 12,180 genes are up-regulated and 10,876 genes are down-regulated. Between H and L, 6182 genes are up-regulated and 1850 genes are down-regulated, which gives a total of 8032 genes. The highest number of genes, that are differentially expressed, was obtained when a comparison was made between CK and H. A total of 43,074 genes were found to be differentially expressed with 26,977 genes up-regulated and 16,097 genes down-regulated. Further analysis of these genes suggests that many of the up-regulated genes are enriched in pathways involved in amino acid metabolism. Besides, 39 transcription factors (TFs) were found to be continuously up-regulated with the increase of drought stress level. Conclusion Taken together, the results indicate that O. taihangensis plants are able to live adaptively under drought stress by responding physiologically and regulating the expression of a substantial number of drought-responsive genes and TFs to avoid adverse effects.