Effect of phytoglobin1 (Pgb1) expression on the regeneration of maize (Zea mays L.) root quiescent centers (QCs) during hypoxia

Maize (Zea mays) root quiescent center (QC) cells deteriorate during hypoxic treatment, halting root growth. Over-expression of the Phytoglobin1 ZmPgb1.1 is known to alleviate these effects through the retention of the auxin flow along the root profile required for QC specification. To elucidate QC-specific hypoxia responses and whether ZmPgb1.1 exercises a direct role on QC stem cells, we performed a QC functionality test. This was done by estimating the ability of QCs to regenerate a root in-vitro in a hypoxic environment. Hypoxia decreased the functionality of the QCs by depressing the expression of several genes participating in the synthesis and response of auxin. This was accompanied by a decrease in DR5 signal in oxygen deprived QCs and a consequent suppression of QC markers and genes of jasmonic acid (JA) synthesis and signaling. Over-expression of ZmPgb1.1 mitigated all these responses. Through pharmacological alterations of auxin and JA (through 1-Naphthaleneacetic acid and methyl jasmonate, respectively), it is demonstrated that both compounds are required for QC functionality under hypoxia, and that JA acts downstream of auxin during QC regeneration. A model is proposed whereby the ZmPgb1.1 maintenance of auxin in hypoxic QCs is determinant for the retention of their functionality, with JA supporting the regeneration of roots from the QCs.