Combined dynamics of physiological and transcriptome analysis reveal key molecular networks of Ca2+-regulated radial growth of radish taproots

Calcium (Ca 2+ ) is crucial for maintaining edible organ productivity and quality in vegetable crops. In agricultural production, radish taproot growth is influenced by Ca 2+ availability, however, the underlying mechanism remains largely unknown. Here, we showed that Ca 2+ promotes the initiation of rapid radial thickening in taproots. Under low-Ca 2+ conditions, this distinct growth pattern was suppressed due to the inhibition of cambial cell proliferation and parenchymal cell expansion in the secondary xylem. By the dynamics of transcriptome analysis, we observed numerous genes related to hormone signaling and cell cycle pathways that responded significantly to different Ca 2+ treatments at the transcriptional level. Furthermore, a Ca 2+ -dependent time-ordered gene co-expression network identified RsaSHR and RsaAGL8 as key transcriptional regulators in these biological processes. This suggests that radish employed a complex regulatory network to integrate hormone action and cell division pathways for regulating secondary xylem development in response to Ca 2+ availability. Importantly, our study identified the regulatory role of RsaAGL8 in altering the expression of RsaICK6 , which might function in regulating parenchymal cell expansion. These results revealed essential roles of RsaSHR and RsaAGL8 for synergizing cambial and parenchymal cell growth, allowing for efficient taproot development under fluctuating Ca 2+ levels, and laying the foundation for genetic improvement of radish.