A peak in global DNA methylation is a key step to initiate the somatic embryogenesis of coconut palm (Cocos nucifera L).

KEY MESSAGE: DNA methylation, morphogenesis and gene expression during the somatic embryogenesis of Coconut are affected by 5-Azacytidine pretreatments, indicating that DNA methylation is an important factor throughout this process. Somatic embryogenesis (SE) is a process that can aid in the production of elite Cocos nucifera palms. It has been well established that epigenetic mechanisms are regulators of cell differentiation programs; however, their role in the coconut somatic embryogenesis has not yet been addressed. To this end, the morphogenetic changes, the global DNA methylation and the expression profiles of the SE-related genes and DNA methyltransferases genes were evaluated during the SE process, with and without the presence of 5-Azacytidine (AzaC). The results show that three days of pretreatments with 15 µM and 20 µM of AzaC significantly increased early somatic embryo formation (four- and tenfold, respectively). A clear peak of the global percentage of DNA methylation (approximately 13%) was determined at the beginning of the culture, followed by a re-establishing stage and a steady increase thereafter; in all cases, the levels of DNA methylation were lower after the pretreatments with AzaC. Additionally, the expression profiles of the SERK, WUS, BBM and LEC genes are modulated during the SE process and the pretreatments with AzaC affect the expression profiles of these genes, even at early stages. Furthermore, increased levels of expression were observed for the genes encoding for DNA methyltransferases (MET, CMT and DRM) at early and late stages of SE, indicating that DNA methylation is an important factor throughout the SE.

Physiological differences and changes in global DNA methylation levels in Agave angustifolia Haw. albino variant somaclones during the micropropagation process.

KEY MESSAGE: Global DNA methylation changes caused by in vitro conditions are associated with the subculturing and phenotypic variation in Agave angustifolia Haw. While the relationship between the development of albinism and in vitro culture is well documented, the role of epigenetic processes in this development leaves some important questions unanswered. During the micropropagation of Agave angustifolia Haw., we found three different phenotypes, green (G), variegated (V) and albino (A). To understand the physiological and epigenetic differences among the somaclones, we analyzed several morphophysiological parameters and changes in the DNA methylation patterns in the three phenotypes during their in vitro development. We found that under in vitro conditions, the V plantlets maintained their CAM photosynthetic capacity, while the A variant showed no pigments and lost its CAM photosynthetic ability. Epigenetic analysis revealed that global DNA methylation increased in the G phenotype during the first two subcultures. However, after that time, DNA methylation levels declined. This hypomethylation correlated with the appearance of V shoots in the G plantlets. A similar correlation occurred in the V phenotype, where an increase of 2 % in the global DNA methylation levels was correlated with the generation of A shoots in the V plantlets. This suggests that an "epigenetic stress memory" during in vitro conditions causes a chromatin shift that favors the generation of variegated and albino shoots.

Physiological, epigenetic, and proteomic responses in Pfaffia glomerata growth in vitro under salt stress and 5-azacytidine.

Plants adjust their complex molecular, biochemical, and metabolic processes to overcome salt stress. Here, we investigated the proteomic and epigenetic alterations involved in the morphophysiological responses of Pfaffia glomerata, a medicinal plant, to salt stress and the demethylating agent 5-azacytidine (5-azaC). Moreover, we investigated how these changes affected the biosynthesis of 20-hydroxyecdysone (20-E), a pharmacologically important specialized metabolite. Plants were cultivated in vitro for 40 days in Murashige and Skoog medium supplemented with NaCl (50 mM), 5-azaC (25 µM), and NaCl + 5-azaC. Compared with the control (medium only), the treatments reduced growth, photosynthetic rates, and photosynthetic pigment content, with increase in sucrose, total amino acids, and proline contents, but a reduction in starch and protein. Comparative proteomic analysis revealed 282 common differentially accumulated proteins involved in 87 metabolic pathways, most of them related to amino acid and carbohydrate metabolism, and specialized metabolism. 5-azaC and NaCl + 5-azaC lowered global DNA methylation levels and 20-E content, suggesting that 20-E biosynthesis may be regulated by epigenetic mechanisms. Moreover, downregulation of a key protein in jasmonate biosynthesis indicates the fundamental role of this hormone in the 20-E biosynthesis. Taken together, our results highlight possible regulatory proteins and epigenetic changes related to salt stress tolerance and 20-E biosynthesis in P. glomerata, paving the way for future studies of the mechanisms involved in this regulation.

Assessment of molecular and epigenetic changes in the albinism of Agave angustifolia Haw.

Albinism in plants is a rare phenomenon that occurs in nature and is characterized by the total or partial loss of photosynthetic pigments. Although progress has been made in understanding the nature of this phenomenon, the precise causes and biological basis are still unexplored. Here, we study the genetic and epigenetic differences between green (G), variegated (V) and albino (A) A. angustifolia Haw. plantlets obtained by in vitro propagation in order to present new insights into albinism from a plant system that offers a unique set of biological phenotypic characteristics. Low transcript levels of genes involved in carotenoids and photosynthesis such as PSY, PDS, LCYƐ, rubS, PEPCase and LHCP suggest a disruption in these processes in albino plants. Due to a high level of genetic similarity being found between the three phenotypes, we analyzed global DNA methylation and different histone marks (H3K4me2, H3K36me2, H3K9ac, H3K9me2 and H3K27me3). Although no significant differences in global 5-methyl deoxicytidine were found, almost a 2-4.5-fold increase in H3K9ac was observed in albino plants in comparison with variegated or green plants, suggesting a change in chromatin compaction related to A. angustifolia albinism.

Structural and phylogenetic analysis of Pto-type disease resistance gene candidates in banana.

The tomato Pto gene encodes a serine/threonine kinase (STK) whose molecular characterization has provided valuable insights into the disease resistance mechanism of tomato and it is considered as a promising candidate for engineering broad-spectrum pathogen resistance in this crop. In this study, a pair of degenerate primers based on conserved subdomains of plant STKs similar to the tomato Pto protein was used to amplify similar sequences in banana. A fragment of approximately 550 bp was amplified, cloned and sequenced. The sequence analysis of several clones revealed 13 distinct sequences highly similar to STKs. Based on their significant similarity with the tomato Pto protein (BLASTX E value <3e-53), seven of them were classified as Pto resistance gene candidates (Pto-RGCs). Multiple sequence alignment of the banana Pto-RGC products revealed that these sequences contain several conserved subdomains present in most STKs and also several conserved residues that are crucial for Pto function. Moreover, the phylogenetic analysis showed that the banana Pto-RGCs were clustered with Pto suggesting a common evolutionary origin with this R gene. The Pto-RGCs isolated in this study represent a valuable sequence resource that could assist in the development of disease resistance in banana.