PaACL silencing accelerates flower senescence and changes the proteome to maintain metabolic homeostasis in Petunia hybrida

Lysine acetylation of histone acetyltransferase adaptor protein ADA2 is a mechanism of metabolic control of chromatin modification in plants

Histone acetylation is a predominant active chromatin mark deposited by histone acetyltransferases (HATs) that transfer the acetyl group from acetyl coenzyme A (acetyl-CoA) to lysine ε-amino groups in histones. GENERAL CONTROL NON-REPRESSED PROTEIN 5 (GCN5) is one of the best-characterized HATs and functions in association with several adaptor proteins such as ADA2 within multiprotein HAT complexes. ADA2-GCN5 interaction increases GCN5 binding to acetyl-CoA and stimulates its HAT activity. It remains unclear whether the HAT activity of GCN5 (which acetylates not only histones but also cellular proteins) is regulated by acetyl-CoA levels, which vary greatly in cells under different metabolic and nutrition conditions. Here we show that the ADA2 protein itself is acetylated by GCN5 in rice cells. Lysine acetylation exposes ADA2 to a specific E3 ubiquitin ligase and reduces its protein stability. In rice plants, ADA2 protein accumulation reversely parallels its lysine acetylation and acetyl-CoA levels, both of which are dynamically regulated under varying growth conditions. Stress-induced ADA2 accumulation could stimulate GCN5 HAT activity to compensate for the reduced acetyl-CoA levels for histone acetylation. These results indicate that ADA2 lysine acetylation that senses cellular acetyl-CoA variations is a mechanism to regulate HAT activity and histone acetylation homeostasis in plants under changing environments.

How far can omics go in unveiling the mechanisms of floral senescence?

Floral senescence is of fundamental interest in understanding plant developmental regulation, it is of ecological and agricultural interest in relation to seed production, and is of key importance to the production of cut flowers. The biochemical changes occurring are well-studied and involve macromolecular breakdown and remobilisation of nutrients to developing seeds or other young organs in the plant. However, the initiation and regulation of the process and inter-organ communication remain to be fully elucidated. Although ethylene emission, which becomes autocatalytic, is a key regulator in some species, in other species it appears not to be as important. Other plant growth regulators such as cytokinins, however, seem to be important in floral senescence across both ethylene sensitive and insensitive species. Other plant growth regulators are also likely involved. Omics approaches have provided a wealth of data especially in ornamental species where genome data is lacking. Two families of transcription factors: NAC and WRKY emerge as major regulators, and omics information has been critical in understanding their functions. Future progress would greatly benefit from a single model species for understanding floral senescence; however, this is challenging due to the diversity of regulatory mechanisms. Combining omics data sets can be powerful in understanding different layers of regulation, but in vitro biochemical and or genetic analysis through transgenics or mutants is still needed to fully verify mechanisms and interactions between regulators.

ACL and HAT1 form a nuclear module to acetylate histone H4K5 and promote cell proliferation

Acetyl-CoA utilized by histone acetyltransferases (HAT) for chromatin modification is mainly generated by ATP-citrate lyase (ACL) from glucose sources. How ACL locally establishes acetyl-CoA production for histone acetylation remains unclear. Here we show that ACL subunit A2 (ACLA2) is present in nuclear condensates, is required for nuclear acetyl-CoA accumulation and acetylation of specific histone lysine residues, and interacts with Histone AcetylTransferase1 (HAT1) in rice. The rice HAT1 acetylates histone H4K5 and H4K16 and its activity on H4K5 requires ACLA2. Mutations of rice ACLA2 and HAT1 (HAG704) genes impair cell division in developing endosperm, result in decreases of H4K5 acetylation at largely the same genomic regions, affect the expression of similar sets of genes, and lead to cell cycle S phase stagnation in the endosperm dividing nuclei. These results indicate that the HAT1-ACLA2 module selectively promotes histone lysine acetylation in specific genomic regions and unravel a mechanism of local acetyl-CoA production which couples energy metabolism with cell division.

The SmMYB36-SmERF6/SmERF115 module regulates the biosynthesis of tanshinones and phenolic acids in salvia miltiorrhiza hairy roots

Tanshinone and phenolic acids are the most important active substances of Salvia miltiorrhiza, and the insight into their transcriptional regulatory mechanisms is an essential process to increase their content in vivo. SmMYB36 has been found to have important regulatory functions in the synthesis of tanshinone and phenolic acid; paradoxically, its mechanism of action in S. miltiorrhiza is not clear. Here, we demonstrated that SmMYB36 functions as a promoter of tanshinones accumulation and a suppressor of phenolic acids through the generation of SmMYB36 overexpressed and chimeric SmMYB36-SRDX (EAR repressive domain) repressor hairy roots in combination with transcriptomic-metabolomic analysis. SmMYB36 directly down-regulate the key enzyme gene of primary metabolism, SmGAPC, up-regulate the tanshinones biosynthesis branch genes SmDXS2, SmGGPPS1, SmCPS1 and down-regulate the phenolic acids biosynthesis branch enzyme gene, SmRAS. Meanwhile, SmERF6, a positive regulator of tanshinone synthesis activating SmCPS1, was up-regulated and SmERF115, a positive regulator of phenolic acid biosynthesis activating SmRAS, was down-regulated. Furthermore, the seven acidic amino acids at the C-terminus of SmMYB36 are required for both self-activating domain and activation of target gene expression. As a consequence, this study contributes to reveal the potential relevance of transcription factors synergistically regulating the biosynthesis of tanshinone and phenolic acid.

Crotonylation versus acetylation in petunia corollas with reduced acetyl-CoA due to PaACL silencing

Protein acetylation and crotonylation are important posttranslational modifications of lysine. In animal cells, the correlation of acetylation and crotonylation has been well characterized and the lysines of some proteins are acetylated or crotonylated depending on the relative concentrations of acetyl-CoA and crotonyl-CoA. However, in plants, the correlation of acetylation and crotonylation and the effects of the relative intracellular concentrations of crotonyl-CoA and acetyl-CoA on protein crotonylation and acetylation are not well known. In our previous study, PaACL silencing changed the content of acetyl-CoA in petunia (Petunia hybrida) corollas, and the effect of PaACL silencing on the global acetylation proteome in petunia was analyzed. In the present study, we found that PaACL silencing did not significantly alter the content of crotonyl-CoA. We performed a global crotonylation proteome analysis of the corollas of PaACL-silenced and control petunia plants; we found that protein crotonylation was closely related to protein acetylation and that proteins with more crotonylation sites often had more acetylation sites. Crotonylated proteins and acetylated proteins were enriched in many common Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. However, PaACL silencing resulted in different KEGG pathway enrichments of proteins with different levels of crotonylation sites and acetylation sites. PaACLB1-B2 silencing did not led to changes in the opposite direction in crotonylation and acetylation levels at the same lysine site in cytoplasmic proteins, which indicated that cytoplasmic lysine acetylation and crotonylation might not depend on the relative concentrations of acetyl-CoA and crotonyl-CoA. Moreover, the global crotonylome and acetylome were weakly positively correlated in the corollas of PaACL-silenced and control plants.

ROS-stimulated Protein Lysine Acetylation Is Required for Crown Root Development in Rice

INTRODUCTION

As signal molecules in aerobic organisms, locally accumulated ROS have been reported to balance cell division and differentiation in the root meristem. Protein posttranslational modifications such as lysine acetylation play critical roles in controlling a variety of cellular processes. However, the mechanism by which ROS regulate root development is unknown. In addition, how protein lysine acetylation is regulated and whether cellular ROS levels affect protein lysine acetylation remain unclear.

OBJECTIVES

We aimed to elucidate the relationship between ROS and protein acetylation by exploring a rice mutant plant that displays a decreased level of ROS in postembryonic crown root (CR) cells and severe defects in CR development.

METHODS

First, proteomic analysis was used to find candidate proteins responsible for the decrease of ROS detected in the wox11 mutant. Then, biochemical, molecular, and genetic analyses were used to study WOX11-regulated genes involved in ROS homeostasis. Finally, acetylproteomic analysis of wild type and wox11 roots treated with or without potassium iodide (KI) and peroxide (H₂O₂) were used to study the effects of ROS on protein acetylation in rice CR cells.

RESULTS

We demonstrated that WOX11 was required to maintain ROS homeostasis by upregulating peroxidase genes in the crown root meristem. Acetylproteomic analysis revealed that WOX11-dependent peroxide (H₂O₂) levels in CR cells promoted lysine acetylation of many non-histone proteins enriched for nitrogen metabolism and peptide/protein synthesis pathways. Further analysis revealed that the redox state affected histone deacetylases (HDACs) activity, which was likely related to the high levels of protein lysine acetylation in CR cells.

CONCLUSION

WOX11-controlled ROS level in CR meristem cells is required for protein lysine acetylation which represents a mechanism of ROS-promoted CR development in rice.

Advances in proteome-wide analysis of plant lysine acetylation

Lysine acetylation (LysAc) is a conserved and important post-translational modification (PTM) that plays a key role in plant physiological and metabolic processes. Based on advances in Lys-acetylated protein immunoenrichment and mass-spectrometric technology, LysAc proteomics studies have been performed in many species. Such studies have made substantial contributions to our understanding of plant LysAc, revealing that Lys-acetylated histones and nonhistones are involved in a broad spectrum of plant cellular processes. Here, we present an extensive overview of recent research on plant Lys-acetylproteomes. We provide in-depth insights into the characteristics of plant LysAc modifications and the mechanisms by which LysAc participates in cellular processes and regulates metabolism and physiology during plant growth and development. First, we summarize the characteristics of LysAc, including the properties of Lys-acetylated sites, the motifs that flank Lys-acetylated lysines, and the dynamic alterations in LysAc among different tissues and developmental stages. We also outline a map of Lys-acetylated proteins in the Calvin-Benson cycle and central carbon metabolism-related pathways. We then introduce some examples of the regulation of plant growth, development, and biotic and abiotic stress responses by LysAc. We discuss the interaction between LysAc and Nα-terminal acetylation and the crosstalk between LysAc and other PTMs, including phosphorylation and succinylation. Finally, we propose recommendations for future studies in the field. We conclude that LysAc of proteins plays an important role in the regulation of the plant life cycle.

Mitochondrial citrate synthase plays important roles in anthocyanin synthesis in petunia

Anthocyanins are important flavonoid pigments in plants. Malonyl CoA is an important intermediate in anthocyanin synthesis, and citrate, formed by citrate synthase (CS) catalysing oxaloacetate, is the precursor for the formation of malonyl-CoA. CS is composed of two isoforms, mitochondrial citrate synthase (mCS), a key enzyme of the tricarboxylic acid (TCA) cycle, and citrate synthase (CSY) localizated in microbodies in plants. However, no CS isoform involvement in anthocyanin synthesis has been reported. In this study, we identified the entire CS family in petunia (Petunia hybrida): PhmCS, PhCSY1 and PhCSY2. We obtained petunia plants silenced for the three genes. PhmCS silencing resulted in abnormal development of leaves and flowers. The contents of citrate and anthocyanins were significantly reduced in flowers in PhmCS-silenced plants. However, silencing of PhCSY1 and/or PhCSY2 did not cause a visible phenotype change in petunia. These results showed that PhmCS is involved in anthocyanin synthesis and the development of leaves and flowers, and that the citrate involved in anthocyanin synthesis mainly derived from mitochondria rather than microbodies in petunia.