Nitric oxide alleviates programmed cell death induced by cadmium in Solanum lycopersicum seedlings through protein S-nitrosylation.

Cadmium (Cd), as a non-essential and toxic heavy metal in plants, has deleterious effects on plant physiological and biochemical processes. Nitric oxide (NO) is one of the most important signaling molecules for plants to response diverse stresses. Here, we found that Cd-induced programmed cell death (PCD) was accompanied by NO bursts, which exacerbated cell death when NO was removed and vice versa. Proteomic analysis of S-nitrosylated proteins showed that the differential proteins in Cd-induced PCD and in NO-alleviated PCD mainly exist together in carbohydrate metabolism and amino acid metabolism, while some of the differential proteins exist alone in metabolism of cofactors and vitamins and lipid metabolism. Meanwhile, S-nitrosylation of proteins in porphyrin and chlorophyll metabolism and starch and sucrose metabolism could explain the leaf chlorosis induced by PCD. Moreover, protein transport protein SEC23, ubiquitinyl hydrolase 1 and pathogenesis-related protein 1 were identified to be S-nitrosylated in vivo, and their expressions were increased in Cd-induced PCD while decreased in NO treatment. Similar results were obtained in tomato seedlings with higher S-nitrosylation. Taken together, our results indicate that NO might be involved in the regulation of Cd-induced PCD through protein S-nitrosylation, especially proteins involved in PCD response.

Role of methylation in vernalization and photoperiod pathway: a potential flowering regulator?

Recognized as a pivotal developmental transition, flowering marks the continuation of a plant's life cycle. Vernalization and photoperiod are two major flowering pathways orchestrating numerous florigenic signals. Methylation, including histone, DNA and RNA methylation, is one of the recent foci in plant development. Considerable studies reveal that methylation seems to show an increasing potential regulatory role in plant flowering via altering relevant gene expression without altering the genetic basis. However, little has been reviewed about whether and how methylation acts on vernalization- and photoperiod-induced flowering before and after FLOWERING LOCUS C (FLC) reactivation, what role RNA methylation plays in vernalization- and photoperiod-induced flowering, how methylation participates simultaneously in both vernalization- and photoperiod-induced flowering, the heritability of methylation memory under the vernalization/photoperiod pathway, and whether and how methylation replaces vernalization/photoinduction to regulate flowering. Our review provides insight about the crosstalk among the genetic control of the flowering gene network, methylation (methyltransferases/demethylases) and external signals (cold, light, sRNA and phytohormones) in vernalization and photoperiod pathways. The existing evidence that RNA methylation may play a potential regulatory role in vernalization- and photoperiod-induced flowering has been gathered and represented for the first time. This review speculates about and discusses the possibility of substituting methylation for vernalization and photoinduction to promote flowering. Current evidence is utilized to discuss the possibility of future methylation reagents becoming flowering regulators at the molecular level.

The Role of Light-Regulated Auxin Signaling in Root Development.

The root is an important organ for obtaining nutrients and absorbing water and carbohydrates, and it depends on various endogenous and external environmental stimulations such as light, temperature, water, plant hormones, and metabolic constituents. Auxin, as an essential plant hormone, can mediate rooting under different light treatments. Therefore, this review focuses on summarizing the functions and mechanisms of light-regulated auxin signaling in root development. Some light-response components such as phytochromes (PHYs), cryptochromes (CRYs), phototropins (PHOTs), phytochrome-interacting factors (PIFs) and constitutive photo-morphorgenic 1 (COP1) regulate root development. Moreover, light mediates the primary root, lateral root, adventitious root, root hair, rhizoid, and seminal and crown root development via the auxin signaling transduction pathway. Additionally, the effect of light through the auxin signal on root negative phototropism, gravitropism, root greening and the root branching of plants is also illustrated. The review also summarizes diverse light target genes in response to auxin signaling during rooting. We conclude that the mechanism of light-mediated root development via auxin signaling is complex, and it mainly concerns in the differences in plant species, such as barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), changes of transcript levels and endogenous IAA content. Hence, the effect of light-involved auxin signaling on root growth and development is definitely a hot issue to explore in the horticultural studies now and in the future.

Effects of Hydrogen Sulfide on Sugar, Organic Acid, Carotenoid, and Polyphenol Level in Tomato Fruit.

Hydrogen sulfide (H2S) is known to have a positive effect on the postharvest storage of vegetables and fruits, but limited results are available on its influence in fruit flavor quality. Here, we presented the effect of H2S on the flavor quality of tomato fruit during postharvest. H2S decreased the content of fructose, glucose, carotene and lycopene but increased that of soluble protein, organic acid, malic acid and citric acid. These differences were directly associated with the expression of their metabolism-related genes. Moreover, H2S treatment raised the contents of total phenolics, total flavonoids and most phenolic compounds, and up-regulated the expression level of their metabolism-related genes (PAL5, 4CL, CHS1, CHS2, F3H and FLS). However, the effects of the H2S scavenger hypotaurine on the above flavor quality parameters were opposite to that of H2S, thus confirming the role of H2S in tomato flavor quality. Thus, these results provide insight into the significant roles of H2S in tomato fruit quality regulation and implicate the potential application of H2S in reducing the flavor loss of tomato fruit during postharvest.

Comprehensive transcriptome analysis unravels the crucial genes during adventitious root development induced by carbon monoxide in Cucumis sativus L.

BACKGROUND: Carbon monoxide (CO) has been reported to be participated in adventitious rooting. However, knowledge about the interrelationship between CO and phytohormones during rooting is obscure. The molecular mechanism of CO-induced rooting is currently unclear. METHODS AND RESULTS: The roles of CO in adventitious rooting in Cucumis sativus L. at the transcriptional level were investigated. The results show that 10 µM hematin (a CO donor) has a significant positive effect on adventitious rooting in cucumber. A total of 1792 differentially expressed genes (DEGs; 1103 up-regulated and 689 down-regulated) were identified in hematin treatment by RNA sequencing analysis. There were 37, 18 and 19 DEGs significantly enriched in plant hormone signal transduction, sucrose and starch metabolism, and phenylalanine metabolism, respectively. Both transcriptome and real-time quantitative PCR results showed that the expressions of AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A and TIF9 promoted the accumulation of IAA, BR, JA and SA in plant hormone signal transduction. The up-regulation of HK3, TPPF, otsB, TPS7, TPS9 and the down-regulation of AGPS1, AGPS3 increased the content of starch and total sugar by mediating the activity of some critical enzymes, including HK, TPS, TPP and AGP. PER47, PER61, PER24, PER66, PER4 and CCR2 increased the lignin content. CONCLUSION: Our results suggest that CO could promote the accumulation of plant hormones, starch, sugar and lignin during adventitious rooting by regulating the expression of some related genes, including AUX22D, IAA6, SAUR21, SAUR24, GH3.5, CYCD3-3, TIFY10a, TIFY10A, TIF9 HK3, otsB, TPS7, TPS9, AGPS1, AGPS3, PER47, PER61, PER24, PER66, PER4, and CCR2. Thus, we provides an interesting candidate gene list for further studies on the molecular mechanisms of adventitious rooting.

Genome-wide identification and expression analysis of serine hydroxymethyltransferase (SHMT) gene family in tomato (Solanum lycopersicum).

Serine hydroxymethyltransferase (SHMT) is one of the most important enzyme families in one-carbon metabolic pathway and photorespiration within plant cells. Recently studies reported the active roles of plant SHMTs in defending abiotic stresses. However, genome-scale analysis of SHMT in tomato is currently unknown. In this study, seven SHMT genes were identified in the tomato genome using a genome-wide search approach. In addition, their physicochemical properties, protein secondary structure, subcellular localization, gene structure, conserved motifs, phylogenetic and collinear relationships were analyzed. Our results demonstrated that tomato SHMT members were divided into two group and four subgroups, and they were conserved with the orthologs of other plants. Analysis of cis-acting elements showed that each of the SlSHMT genes contained different kinds of hormones and stress-related cis-acting elements in their promoter regions. Finally, qRT-PCR analysis indicated that SlSHMTs were expressed at different levels in different tissues, and they responded to UV, cold, heat, NaCl, H2O2, ABA and PEG treatments. These results provided definite evidence that SlSHMTs might involve in growth, development and stress responses in tomato, which laid a foundation for future functional studies of SlSHMTs.