Auxin and abscisic acid play important roles in promoting glucose metabolism of reactivated young kernels of maize (Zea mays L.).

In maize, young kernels that are less competitive and have poor sink activity often abort. Studies have indicated that such poor competitiveness depends, in part, on the regulation by auxin (IAA) and abscisic acid (ABA). However, the mechanisms for such effects remain unclear. We used pollination-blocking and hand-pollination treatments accompanied by multi-omics and physiological tests, to identify underlying mechanism by which IAA and ABA, along with sugar signaling affect kernel development. Results showed that preventing pollination of the primary ears reactivated kernels in the secondary ears and altered both sugar metabolism and hormone signaling pathways. This was accompanied by increased enzyme activities in carbon metabolism and concentrations of glucose and starch, as well as increased levels of IAA and decreased levels of ABA in the reactivated kernels. Positive and negative correlations were observed between IAA, ABA contents and cell wall invertase (CWIN) activity, and glucose contents, respectively. In vitro culture revealed that the expression of genes involved in glucose utilization was upregulated by IAA, but downregulated by ABA. IAA could promote the expression of ABA signaling genes ZmPP2C9 and ZmPP2C13 but downregulated the expression of Zmnced5, an ABA biosynthesis gene, and ZmSnRK2.10, which is involved in ABA signal transduction. However, these genes showed opposite trends when IAA transport was inhibited. To summarize, we suggest a regulatory model for how IAA inhibits ABA metabolism by promoting the smooth utilization of glucose in reactivated young kernels. Our findings highlight the importance of IAA in ABA signaling by regulating glucose production and transport in maize.