The Transcription Factor MiMYB8 Suppresses Peel Coloration in Postharvest 'Guifei' Mango in Response to High Concentration of Exogenous Ethylene by Negatively Modulating MiPAL1.

Anthocyanin accumulation is regulated by specific genes during fruit ripening. Currently, peel coloration of mango fruit in response to exogenous ethylene and the underlying molecular mechanism remain largely unknown. The role of MiMYB8 on suppressing peel coloration in postharvest 'Guifei' mango was investigated by physiology detection, RNA-seq, qRT-PCR, bioinformatics analysis, yeast one-hybrid, dual-luciferase reporter assay, and transient overexpression. Results showed that compared with the control, low concentration of exogenous ethylene (ETH, 500 mg·L-1) significantly promoted peel coloration of mango fruit (cv. Guifei). However, a higher concentration of ETH (1000 mg·L-1) suppressed color transformation, which is associated with higher chlorophyll content, lower a* value, anthocyanin content, and phenylalanine ammonia-lyase (PAL) activity of mango fruit. M. indica myeloblastosis8 MiMYB8 and MiPAL1 were differentially expressed during storage. MiMYB8 was highly similar to those found in other plant species related to anthocyanin biosynthesis and was located in the nucleus. MiMYB8 suppressed the transcription of MiPAL1 by binding directly to its promoter. Transient overexpression of MiMYB8 in tobacco leaves and mango fruit inhibited anthocyanin accumulation by decreasing PAL activity and down-regulating the gene expression. Our observations suggest that MiMYB8 may act as repressor of anthocyanin synthesis by negatively modulating the MiPAL gene during ripening of mango fruit, which provides us with a theoretical basis for the scientific use of exogenous ethylene in practice.

Characterization and expression analysis of basic leucine zipper (bZIP) transcription factors responsive to chilling injury in peach fruit.

BACKGROUND: Peach (Prunus persica L.) is prone to chilling injury as exhibited by inhibition of the ethylene production, failure in softening, and the manifestation of internal browning. The basic leucine zipper (bZIP) transcription factors play an essential role in regulatory networks that control many processes associated with physiological, abiotic and biotic stress responses in fruits. Formerly, the underlying molecular and regulatory mechanism of (bZIP) transcription factors responsive to chilling injury in peach fruit is still elusive. METHODS AND RESULTS: In the current experiment, the solute peach 'Zhongyou Peach No. 13' was used as the test material and cold storage at low temperature (4 °C). It was found that long-term low-temperature storage induced the production of ethylene, the hardness of the pulp decreased, and the low temperature also induced ABA accumulation. The changes of ABA and ethylene in peach fruits during low-temperature storage were clarified. Since the bZIP transcription factor is involved in the regulation of downstream pathways of ABA signals, 47 peach bZIP transcription factor family genes were identified through bioinformatics analysis. Further based on RT-qPCR analysis, 18 PpbZIP genes were discovered to be expressed in refrigerated peach fruits. Among them, the expression of PpbZIP23 and PpbZIP25 was significantly reduced during the refrigeration process, the promoter analysis of these genes found that this region contains the MYC/MYB/ABRES binding element, but not the DRES/CBFS element, indicating that the expression may be regulated by the ABA-dependent cold induction pathway, thereby responding to chilling injury in peach fruit. CONCLUSIONS: Over investigation will provide new insights for further postharvest protocols related to molecular changes during cold storage and will prove a better cope for chilling injury.

Transcriptome analysis reveals pathogenesis-related gene 1 pathway against salicylic acid treatment in grapevine (Vitis vinifera L).

Salicylic acid (SA) is a well-studied phenolic plant hormone that plays an important role in plant defense against the hemi-biothrophic and biothrophic pathogens and depends on the living cells of host for the successful infection. In this study, a pathogenesis test was performed between Vitis davidii and V. vinifera cultivars against grape white rot disease (Coniella diplodiella). V. davidii was found to be resistant against this disease. SA contents were found to be higher in the resistant grape cultivar after different time points. RNA-seq analysis was conducted on susceptible grapevine cultivars after 12, 24, and 48 h of SA application with the hypothesis that SA may induce defense genes in susceptible cultivars. A total of 511 differentially expressed genes (DEGs) were identified from the RNA-seq data, including some important genes, VvWRKY1/2, VvNPR1, VvTGA2, and VvPR1, for the SA defense pathway. DEGs related to phytohormone signal transduction and flavonoid biosynthetic pathways were also upregulated. The quantitative real-time PCR (qRT-PCR) results of the significantly expressed transcripts were found to be consistent with the transcriptome data, with a high correlation between the two analyses. The pathogenesis-related gene 1 (VvPR1), which is an important marker gene for plant defense, was selected for further promoter analysis. The promoter sequence showed that it contains some important cis-elements (W-box, LS7, as-1, and TCA-element) to recruit the transcription factors VvWRKY, VvNPR1, and VvTGA2 to express the VvPR1 gene in response to SA treatment. Furthermore, the VvPR1 promoter was serially deleted into different fragments (-1,837, -1,443, -1,119, -864, -558, -436, and -192 ) bp and constructed vectors with the GUS reporter gene. Deletion analysis revealed that the VvPR1 promoter between -1837 bp to -558 bp induced significant GUS expression with respect to the control. On the basis of these results, the -558 bp region was assumed to be an important part of the VvPR1 promoter, and this region contained the important cis-elements related to SA, such as TCA-element (-1,472 bp), LS7 (-1,428 bp), and as-1 (-520 bp), that recruit the TFs and induce the expression of the VvPR1 gene. This study expanded the available information regarding SA-induced defense in susceptible grapes and recognized the molecular mechanisms through which this defense might be mediated.

Effect of Salinity Stress on Germination, Seedling Growth, Mineral Uptake and Chlorophyll Contents of Three Cucurbitaceae Species

Abstract This study was performed to screen out the various species of 'Cucurbitaceae' family, musk melon (Kalash and Durga), bottle gourd (Crystal Long and Nuefield) and squash (Green Round, and Squash Malika) against the salt stress. All genotypes were treated with five different levels of NaCl (T0 = control, T1 = 1.5 dS m-1, T2 = 3.0 dS m-1, T3 = 4.5 dS m-1 and T4 = 6.0 dS m-1) and half strength of Hoagland's nutrients solution as the base nutrient solution. Results showed that the bottle gourd varieties "Nuefield" and "Crystal Long" performed best by maintaining the highest germination (93.2% and 85.6%), number of leaves per plant (4.5 and 5.7), shoot length (16.84 cm and 16.14 cm), root length (13.48 cm and 13.00 cm), plant fresh weight (942.2 g and 918.6 g), plant dry weight (118.4 g and 107.5 g), leaf area (171.2 cm2 and 169.1 cm2), chlorophyll content (3.5 μg/cm-2 and 3.4 μg/cm-2) with low chloride (1.57 ppm and 1.59 ppm) and sodium content (0.47 ppm and 0.51 ppm) under salt stress followed by varieties of Squash (Green Round, and Squash Malika) and musk melon (Kalash and Durga). It was also found that a higher level of salinity (4.5 dS m-1 and 6.0 dS m-1) has more adverse effects on the performance of all selected genotypes. Conclusively, it can be recommended that as compared to all tested species, bottle gourd varieties "Nuefield" and "Crystal Long" have the ability to withstand against salinity stress and should be planted under salt stress conditions.