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Originating in the subtropics, cucumbers require warm weather and plenty of light, low light inhibits the growth of cucumbers. For cucumbers to efficiently absorb light energy in low light, chlorophyll synthesis is necessary. Oxygenase for chlorophyllate is encoded by CsCAO. RNA interference (RNAi) was used to reduce CsCAO expression in cucumber, reduced chlorophyll b content and Fv/Fm (maximal photochemical efficiency of photosystem II) were found in RNAi- CsCAO lines. The Arabidopsis Atcao mutant lacks chlorophyll b and has a low Fv/Fm, but overexpressing CsCAO restored the mutant's phenotype. CsCAO gene expression was found to be upregulated in the presence of low light. The Y1H screening assay revealed that CsHsfA6b and CsBLH4 were potential CsCAO expression regulators. The results of the Y1H, LUC/REN, and EMSA assays confirmed that only CsBLH4 can bind to the CsCAO promoter. Furthermore, like Atcao , the Atblh4 mutant had low chlorophyll b content and Fv/Fm. CsCAO overexpression in the Atblh4 mutant increased the content of chlorophyll b and Fv/Fm, especially under low light conditions. CsBLH4 targeting CsCAO was found to positively regulate chlorophyll b synthesis and photosynthetic capacity in cucumber under low light conditions in our study. • Low light promoted the accumulation of chlorophyll b by up-regulating the transcription level of CsCAO. • It clarified the regulatory mechanism of BLH family member involved in chlorophyll b synthesis. • The synthesis of chlorophyll plays an important role in the response of cucumber to low light stress. [ABSTRACT FROM AUTHOR]

Tomato fruits were treated by exogenous melatonin. The effect of melatonin on ethylene biosynthesis, ethylene perception, and ethylene signalling may contribute to fruit ripening and quality improvement in tomato.In this study, the effect of melatonin on the postharvest ripening and quality improvement of tomato fruit was carried out. The tomatoes were immersed in exogenous melatonin for 2h, and then the related physiological indicators and the expression of genes during post-harvest life were evaluated. Compared with control check (CK), the 50 µM melatonin treatment significantly increased lycopene levels by 5.8-fold. Meanwhile, the key genes involved in fruit colour development, including phytoene synthase1 (PSY1) and carotenoid isomerase (CRTISO), showed a 2-fold increase in expression levels. The rate of water loss from tomato fruit also increased 8.3%, and the expression of aquaporin genes, such as SlPIP12Q, SlPIPQ, SlPIP21Q, and SlPIP22, was up-regulated 2- to 3-fold under 50 µM melatonin treatment. In addition, 50 µM melatonin treatment enhanced fruit softening, increased water-soluble pectin by 22.5%, and decreased protopectin by 19.5%. The expression of the cell wall modifying proteins polygalacturonase (PG), pectin esterase1 (PE1), β-galactosidase (TBG4), and expansin1 (Exp1) was up-regulated under 50 µM melatonin treatment. Melatonin increased ethylene production by 27.1%, accelerated the climacteric phase, and influenced the ethylene signalling pathway. Alteration of ethylene production correlated with altered 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS4) expression. The expression of ethylene signal transduction-related genes such as NR, SlETR4, SlEIL1, SlEIL3, and SlERF2, was enhanced by 50 µM melatonin. The effect of melatonin on ethylene biosynthesis, ethylene perception, and ethylene signalling may contribute to fruit ripening and quality improvement in tomato. This research may promote the application of melatonin on postharvest ripening and quality improvement of tomato fruit as well as other horticultural productions in the future. [ABSTRACT FROM AUTHOR]

In plants heme containing cytochrome P450 (P450) is a superfamily of monooxygenases that catalyze the addition of one oxygen atom from O into a substrate, with a substantial reduction of the other atom to water. The function of P450 families is attributed to chemical defense mechanism under terrestrial environmental conditions; several are involved in secondary and hormone metabolism. However, the evolutionary relationships of P450 genes in Panax ginseng remain largely unknown. In the present study, data mining methods were implemented and 116 novel putative P450 genes were identified from Expressed Sequence Tags (ESTs) of a ginseng database. These genes were classified into four clans and 22 families by sequence similarity conducted at amino acid level. The representative putative P450 sequences of P. ginseng and known P450 family from other plants were used to construct a phylogenetic tree. By comparing with other genomes, we found that most of the P450 genes from P. ginseng can be found in other dicot species. Depending on P450 family functions, seven P450 genes were selected, and for that organ specific expression, abiotic, and biotic studies were performed by quantitative reverse transcriptase-polymerase chain reaction. Different genes were found to be expressed differently in different organs. Biotic stress and abiotic stress transcript level was regulated diversely, and upregulation of P450 genes indicated the involvement of certain genes under stress conditions. The upregulation of the P450 genes under methyl jasmonate and fungal stress justifies the involvement of specific genes in secondary metabolite biosynthesis. Our results provide a foundation for further elucidating the actual function and role of P450 involved in various biochemical pathways in P. ginseng. [ABSTRACT FROM AUTHOR]