Abstract

The root serves as an essential organ in plant growth by taking up nutrients and water from the soil and supporting the rest of the plant body. Some plant species utilize roots as storage organs. Sweet potatoes (Ipomoea batatas), cassava (Manihot esculenta), and radish (Raphanus sativus), for example, are important root crops. However, how their root growth is regulated remains unknown. In this study, we characterized the relationship between cambium and radial root growth in radish. Through a comparative analysis with Arabidopsis root expression data, we identified putative cambium-enriched transcription factors in radish and analysed their expression in representative inbred lines featuring distinctive radial growth. We found that cell proliferation activities in the cambium positively correlated with radial growth and final yields of radish roots. Expression analysis of candidate transcription factor genes revealed that some genes are differentially expressed between inbred lines and that the difference is due to the distinct cytokinin response. Taken together, we have demonstrated for the first time, to the best of our knowledge, that cytokinin-dependent radial growth plays a key role in the yields of root crops.

Highlights

  • Vascular plants are characterized by their dynamic and indeterminate growth in both apical and radial directions

  • We have demonstrated for the first time, to the best of our knowledge, that cytokinindependent radial growth plays a key role in the yields of root crops

  • Our study suggests that the regulation of cambial cell division plays an essential role in radial root growth, and that cytokinin and its downstream transcription factors contribute to this process as key components

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Summary

Introduction

Vascular plants are characterized by their dynamic and indeterminate growth in both apical and radial directions. Undifferentiated cells in the cambium undergo asymmetric cell divisions in anticlinal or periclinal directions to generate daughter cells that become a part of the xylem or phloem tissues. Several environmental components such as temperature, photoperiod, and precipitation affect the secondary growth driven by the cambium (Antonova and Stasova, 1997; Begum et al, 2013). Changes in auxin distribution seem to affect the orientation of cambial initials in response to wounding (Kramer et al, 2008). The initiation of latewood formation and the cessation of cambial cell division are not caused by changes in auxin concentration in the cambium of Scots pine (Uggla et al, 2001), indicating the involvement of other plant hormones in these processes.

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