Hormones and carbohydrates synergistically regulate the formation of swollen roots in a Chinese cabbage translocation line

Abstract

The genus Brassica contains a rich diversity of species and morphological types, including leaf, root, and oil crops, all of which show substantial phenotypic variation. Both Chinese cabbage and cabbage are typical leaf-type crops with normal roots. We created translocation lines based on interspecific crosses between Chinese cabbage and cabbage and identified qdh225, which exhibited a swollen-root phenotype. The swollen root of qdh225 contained a large number of granular substances, and the formation of its irregular morphological tissue was caused by a thickening of the phloem. Transcriptomic and metabolomic data suggested that differential expression of genes encoding nine types of enzymes involved in starch and sucrose metabolism caused changes in starch synthesis and degradation in the swollen root. These genes jointly regulated sucrose and starch levels, leading to significant enrichment of starch and soluble proteins in the swollen root and a reduction in the content of soluble sugars such as d-glucose and trehalose 6-phosphate. A significant increase in auxin (IAA) and abscisic acid (ABA) contents and a decrease in gibberellin (GA) content in the swollen root likely promoted the differential expression of genes associated with hormone signal transduction, thereby regulating the development of the swollen root. Taken together, our data suggest that accumulation of IAA and ABA and reduction in GA promote swollen root formation by regulating hormone-mediated signaling, leading to a thickening of phloem, root enlargement, and substantial accumulation of starch and soluble proteins. The latter provide materials, energy, and nutrient sources for the development of swollen roots.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 31930098 and 32172560), the Hebei Provincial Natural Science Fund for Distinguished Young Scholars (Grant No. C2020204063), and the Innovative Research Group Project of Hebei Natural Science Foundation (Grant No. C2020204111). We appreciate the linguistic assistance provided by A&L Scientific Editing (www.alpublish.com) during the preparation of this manuscript.

Author contributions

S.S., A.G., W.M., and S.X. conceived and designed the experiment; X.R., D.L., and Y.X. carried out the experiments; X.R., W.M., S.X., Y.W., D.F., J.Z., X.C., and S.L. analyzed data; X.R. and W.M. prepared the manuscript; X.R., W.M., S.X., A.G., and S.S. wrote the paper; and all of the authors read and approved the final manuscript.

Data availability

The RNA-seq datasets for qdh225 and 85-1 have been deposited at the NCBI Sequence Read Archive under accession number PRJNA913444.

Conflict of interest

The authors have no conflict of interest to declare.

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