The MdMYB16/MdMYB1-miR7125-MdCCR module regulates the homeostasis between anthocyanin and lignin biosynthesis during light induction in apple.

Light induces anthocyanin accumulation and hence decides the coloration of apple fruit. It also plays a key role in regulating the biosynthesis of other secondary metabolites. However, the crosstalk between anthocyanin and lignin metabolism during light induction, which affects the edible quality and visual quality of apple fruit, respectively, have rarely been characterized. In this study, we identified and functionally elucidated the roles of miR7125 and its target, cinnamoyl-coenzyme A reductase gene (CCR), in regulating the homeostasis between anthocyanin and lignin biosynthesis during light induction. Overexpressing miR7125 or inhibiting CCR transiently in apple fruit promoted anthocyanin biosynthesis but reduced lignin production under light-induced conditions. Consistently, opposite results were observed under the background of repressed miR7125 or overexpressed CCR. We found that the repressor MdMYB16 and the activator MdMYB1 bound to the miR7125 promoter. Transient repression of MdMYB16 upregulated miR7125 expression significantly, accompanied by decreased levels of MdCCR transcript, resulting in a reduction in the lignin biosynthesis and an increase in anthocyanin accumulation. However, transient overexpression of MdMYB16 produced the opposite effects to MdMYB16-RNAi. The results reveal a novel mechanism by which the MdMYB16/MdMYB1-miR7125-MdCCR module collaboratively regulates homeostasis between anthocyanin and lignin biosynthesis under light induction in apple.

Animal wastes as fertilizers enhance growth of young walnut trees under soil drought conditions.

BACKGROUND: Using nutrient-rich animal wastes as organic fertilizers in agricultural practices is a sustainable method for soil amendment and avoiding environmental pollution. In order to evaluate their practical effect, we applied different proportions of animal waste as fertilizers to wet or dry soils that were either planted or not planted with young walnut trees. RESULTS: The results showed that animal waste could increase soil C accumulation and carbon to nitrogen (C/N) ratio and reduce soil organic nitrogen and total nitrogen contents as well as the nitrogen to phosphorus (N/P) ratio in the planted group soil. This framework of soil C and N composition (a high C/N ratio) resulted in high N and Mg contents as well as high Cu and Zn contents in the leaves of the young trees as well as a high dry matter weight/leaf N ratio, causing increased leaf photosynthesis, reduced transpiration and relatively high water use efficiency under soil drought conditions. Also, animal wastes as fertilizers caused the branching of walnut to switch from elongation growth to thickening growth under soil drought conditions. CONCLUSIONS: Principal component analysis and redundancy analysis demonstrated the mechanism by which the soil C/N ratio mediates the flux of available nutrients from the soil to the plant and thereby regulates plant dry matter accumulation and branching architecture under soil drought conditions. The results of this study provide new insights into the improvement of hilly soils using animal waste. © 2020 Society of Chemical Industry.

MiR399d and epigenetic modification comodulate anthocyanin accumulation in Malus leaves suffering from phosphorus deficiency.

Inorganic phosphorus (Pi) deficiency induces anthocyanin accumulation in the leaves of some plant species; however, the molecular mechanisms underlying this phenomenon have not been well characterized. Here, we showed that microRNA399d (miR399d), high-affinity Pi transporter McPHT1;4, and McMYB10 are strongly induced in Malus leaves suffering from Pi deficiency. By culturing explants of transiently transformed plants in MS medium under conditions of Pi sufficiency and Pi deficiency, miR399d and McPHT1;4 were shown to play essential roles in the response to Pi deficiency and to play positive roles in the regulation of anthocyanin biosynthesis. Silencing of McHDA6 expression and treatment with the inhibitor trichostatin A suggested that the low expression of McHDA6 simultaneously reduced the transcription of McMET1 and decreased the methylation level of the McMYB10 promoter; however, the expression of McMYB10 and anthocyanin content were increased. Bimolecular fluorescence complementation and yeast two-hybrid assays revealed that McHDA6 binds directly to McMET1 through its BAH2 and DNMT1-RFD domains. Based on the results of our study, we propose a mechanism for the molecular regulation of anthocyanin biosynthesis, namely, the miR399d and epigenetic modification comodulation model, to explain the phenomenon in which leaves turn red under conditions of Pi deficiency.