Genomic Responses Associated with Drought Stress in Walnut as Revealed Transcriptome Sequencing

Walnut production is challenged by abiotic stresses. We investigated the leaf transcriptome responses of walnut under control and drought stress in 9 and 18 days. We identified 921, 1035 differentially expressed genes (DEGs) between control and drought stress groups in 9 and 18-day, respectively. In control and drought stress conditions DEGs were significantly enriched into the abscisic acid biosynthesis, regulation of stomata closure, leaf morphogenesis, carbohydrate metabolism, oxidative stress, cell wall macromolecule catabolism, and secondary metabolite biosynthesis pathways. We confirmed our RNA-Seq data using quantitative real-time PCR (qPCR) of six candidate genes. Our results indicated that more complicated transcript regulation of drought responses following prolong exposure to drought stress. In general, walnut activated more tolerance mechanisms 18 days after drought stress. Findings of this research would be useful for future studies on breeding for drought tolerance of Persian walnut and related species.

Triterpenoids Biosynthesis Regulation for Leaf Coloring of Wheel Wingnut (Cyclocaryapaliurus)

Cyclocaryapaliurus leaves are rich in triterpenoids with positive results in the treatment of diabetes, antioxidation, and scavenging free radicals. C. paliurus red leaves have been found to contain higher flavonoids including anthocyanin, however, the triterpenoids accumulation pattern is still unclear. For the purpose of researching the triterpenoid accumulating mechanism during red new leaf development, transcriptome and metabolome analysis was conducted during C. paliurus the red leaf development process. The results uncovered that most triterpenoid ingredients were found to accumulate during leaves turning green, while the unique ingredients content including cyclocaric acid A, cyclocarioside I, cyclocarioside Ⅱand cyclocarioside Ⅲ decreased or remained unchanged. Functional structure genes (hydroxymethylglutaryl-CoA synthase, hydroxymethylglutaryl-CoA reductase, and farnesyl-diphosphate synthase) were identified for promoting triterpenoids accumulation mainly in the mevalonic acid pathway (MVA). Moreover, glycosyltransferase (UGT73C, UGT85A, and UGT85K) was also found attributed to triterpenoids accumulation. These findings provide information for a better understanding of the triterpenoid biosynthesis mechanism during leaf development and will be useful for targeted breeding.

MurA escape mutations uncouple peptidoglycan biosynthesis from PrkA signaling

Gram-positive bacteria are protected by a thick mesh of peptidoglycan (PG) completely engulfing their cells. This PG network is the main component of the bacterial cell wall, it provides rigidity and acts as foundation for the attachment of other surface molecules. Biosynthesis of PG consumes a high amount of cellular resources and therefore requires careful adjustments to environmental conditions.An important switch in the control of PG biosynthesis of Listeria monocytogenes, a Gram-positive pathogen with a high infection fatality rate, is the serine/threonine protein kinase PrkA. A key substrate of this kinase is the small cytosolic protein ReoM. We have shown previously that ReoM phosphorylation regulates PG formation through control of MurA stability. MurA catalyzes the first step in PG biosynthesis and the current model suggests that phosphorylated ReoM prevents MurA degradation by the ClpCP protease. In contrast, conditions leading to ReoM dephosphorylation stimulate MurA degradation. How ReoM controls degradation of MurA and potential other substrates is not understood. Also, the individual contribution of the ∼20 other known PrkA targets to PG biosynthesis regulation is unknown.We here present murA mutants which escape proteolytic degradation. The release of MurA from ClpCP-dependent proteolysis was able to constitutively activate PG biosynthesis and further enhances the intrinsic cephalosporin resistance of L. monocytogenes. This activation required the RodA3/PBP B3 transglycosylase/transpeptidase pair as additional effectors of the PrkA signaling route. One murA escape mutation not only fully rescued an otherwise non-viable prkA mutant during growth in batch culture and inside macrophages but also overcompensated cephalosporin hypersensitivity. Our data collectively indicate that the main purpose of PrkA-mediated signaling in L. monocytogenes is control of MurA stability during extra- and intracellular growth. These findings have important implications for the understanding of PG biosynthesis regulation and β-lactam resistance of L. monocytogenes and related Gram-positive bacteria.Author SummaryPeptidoglycan (PG) is the main component of the bacterial cell wall and many of the PG synthesizing enzymes are antibiotic targets. We previously have discovered a new signaling route controlling PG production in the human pathogen Listeria monocytogenes. This route also determines the intrinsic resistance of L. monocytogenes against cephalosporins, a group of β-lactam antibiotics. Signaling involves PrkA, a membrane-embedded protein kinase, that is activated during cell wall stress to phosphorylate its target ReoM. Depending on its phosphorylation, ReoM activates or inactivates PG production by controlling the proteolytic stability of MurA, which catalyzes the first step in PG biosynthesis. MurA degradation depends on the ClpCP protease and we here have isolated murA mutations that escape this degradation. Using these mutants, we could show that regulation of PG biosynthesis through control of MurA stability is the primary purpose of PrkA-mediated signaling in L. monocytogenes. Further experiments identified the transglycosylase RodA and the transpeptidase PBP B3 as additional effectors of PrkA signaling. Our results suggest that both proteins act together to translate the signals received by PrkA into intensification of PG biosynthesis. These findings shed new light on the regulation of PG biosynthesis in Gram-positive bacteria with intrinsic β-lactam resistance.

New Insights on the Regulation of Glucosinolate Biosynthesis via COP1 and DELLA Proteins in Arabidopsis Thaliana

The biosynthesis of defensive secondary metabolites, such as glucosinolates (GSLs), is a costly process, which requires nutrients, ATP, and reduction equivalents, and, therefore, needs well-orchestrated machinery while coordinating defense and growth. We discovered that the key repressor of light signaling, the CONSTITUTIVE PHOTOMORPHOGENIC 1/SUPPRESSOR OF PHYTOCHROME A-105 (COP1/SPA) complex, is a crucial component of GSL biosynthesis regulation. Various mutants in this COP1/SPA complex exhibited a strongly reduced level of GSL and a low expression of jasmonate (JA)-dependent genes. Furthermore, cop1, which is known to accumulate DELLA proteins in the dark, shows reduced gibberellin (GA) and JA signaling, thereby phenocopying other DELLA-accumulating mutants. This phenotype can be complemented by a dominant gain-of-function allele of MYC3 and by crossing with a mutant having low DELLA protein levels. Hence, SPA1 interacts with DELLA proteins in a yeast two-hybrid screen, whereas high levels of DELLA inhibit MYC function and suppress JA signaling. DELLA accumulation leads to reduced synthesis of GSL and inhibited growth. Thus, the COP1/SPA-mediated degradation of DELLA not only affects growth but also regulates the biosynthesis of GSLs.

Transcriptomic analysis reveals anthocyanin biosynthesis regulation in blueberry (Vaccinium ashei) fruit

Blueberry (Vaccinium ashei) is a popular fruit due to its high anthocyanin content. This study aimed to analyze the transcriptome profile of V. ashei cv. ‘Brightwell’ fruits at different stages of development. A total of 314.26 GB of clean data were obtained and de novo assembled into 254,196 unigenes. In comparisons between the early and late stages of fruit ripening, 27 genes (including PAL, CHS, F3H, F3ʹH, F3ʹ5ʹH, LDOX, etc.) were found to cover the main steps in the anthocyanin biosynthesis pathway. Most of these genes were highly expressed in the late stage of fruit development, suggesting that anthocyanin mainly accumulate in the late stage. During the late stage of fruit development, most structural and regulatory genes such as F3ʹ5ʹH and F3ʹH, which are involved in the anthocyanin biosynthetic pathway, were upregulated, causing the fruit to turn blue. Decreased expression of a large number of chloroplast-related genes during the fruit ripening period could explain why the green fruit color fades over time. Additionally, abscisic acid and ethylene may play positive roles in promoting fruit ripening and anthocyanin accumulation. This research reveals the transcriptomic characteristics of immature and mature fruits and enhances our understanding of the molecular mechanisms of anthocyanin biosynthesis and accumulation in blueberry fruit.