| Summary: | Cassava storage roots are among the most important root crops worldwide and represent one of the
most consumed staple foods in Sub-Saharan Africa. The vegetatively propagated tropical shrub can
form many starchy tuberous roots from its stem. These storage roots are formed through the
activation of secondary root growth processes. However, the underlying genetic regulation of
storage root development is largely unknown. Here we report on distinct structural and
transcriptional changes occurring during the early phases of storage root development.
A pronounced increase in auxin-related transcripts and the transcriptional activation of secondary
growth factors, as well as a decrease in gibberellin-related transcripts was observed during the early
stages of secondary root growth. This was accompanied by increased cell wall biosynthesis,
increased most notably during the initial xylem expansion within the root vasculature. Starch storage
metabolism was activated only after the formation of the vascular cambium. The formation of nonlignified xylem parenchyma cells and the activation of starch storage metabolism coincided with
increased expression of the KNOX/BEL genes KNAT1, PENNYWISE and POUND-FOOLISH, indicating
their importance for proper xylem parenchyma function.
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