ABSTRACT
Macadamia nuts are one of the most important economic food items in the world. Pericarp thickness and flavonoid composition are the key quality traits of Macadamia nuts, but the underlying mechanism of pericarp formation is still unknown. In this study, three varieties with significantly different pericarp thicknesses, namely, A38, Guire No.1, and HAES 900, at the same stage of maturity, were used for transcriptome analysis, and the results showed that there were significant differences in their gene expression profile. A total of 3837 new genes were discovered, of which 1532 were functionally annotated. The GO, COG, and KEGG analysis showed that the main categories in which there were significant differences were flavonoid biosynthesis, phenylpropanoid biosynthesis, and the cutin, suberine, and wax biosynthesis pathways. Furthermore, 63 MiMYB transcription factors were identified, and 56 R2R3-MYB transcription factors were clustered into different subgroups compared with those in Arabidopsis R2R3-MYB. Among them, the S4, S6, and S7 subgroups were involved in flavonoid biosynthesis and pericarp formation. A total of 14 MiMYBs' gene expression were verified by RT-qPCR analysis. These results provide fundamental knowledge of the pericarp formation regulatory mechanism in macadamia nuts.
Subject(s)
Gene Expression Profiling , Gene Expression Regulation, Plant , Macadamia , Nuts , Plant Proteins , Transcription Factors , Transcriptome , Macadamia/genetics , Macadamia/metabolism , Plant Proteins/genetics , Plant Proteins/metabolism , Gene Expression Profiling/methods , Nuts/genetics , Nuts/metabolism , Transcription Factors/genetics , Transcription Factors/metabolism , Transcriptome/genetics , Flavonoids/biosynthesis , Flavonoids/metabolism , Multigene Family , Arabidopsis/genetics , Arabidopsis/metabolism , PhylogenyABSTRACT
Macadamia nut plantings in China are expanding year by year. In order to breed and promote superior varieties, this study analyzed the effects of different rootstocks and scions on the survival rate of grafted seedlings, and then selected the best substrate composition for plant growth. The results showed that the survival rate of the HAES788 variety as rootstock and Guire No. 1 as scion was the highest, reaching 96%. The optimal grafting time in December was better than that in March. Furthermore, among 16 substrate formulations, T12, T13, T15, and T16 had advantages of agglomerated soil and more well-developed root systems compared to the CK made of loess. The plant height, stem diameter, leaf length, leaf width, and dry weight of the aboveground and underground parts of the grafted seedlings planted in these substrate formulations were significantly higher than those plants planted in the CK. In addition, the substrate formulations T12, T13, T15, and T16 significantly improved the organic matter, total nitrogen, and total potassium content of the substrate soils, but little improvement was observed for total phosphorus content after 13 months. Overall, macadamia grafting times are best in December, with HAES788 and Guire No. 1 being the best rootstock and scion. The optimal substrate formulations are T12, T13, T15, and T16. This study provides a solid foundation for the production of high-quality macadamia plants.