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Modified gibberellin (GA) signaling leads to semi-dwarfism with low nitrogen (N) use efficiency (NUE) in crops. An understanding of GA-mediated N uptake is essential for the development of crops with improved NUE. The function of GA in modulating N uptake capacity and nitrate (NO3−) transporters (NRTs) was analyzed in the GA synthesis-deficient mutant zmga3ox grown under low (LN) and sufficient (SN) N conditions. LN significantly suppressed the production of GA1, GA3, and GA4, and the zmga3ox plants showed more sensitivity in shoots as well as LN stress. Moreover, the higher anthocyanin accumulation and the decrease of chlorophyll content were also recorded. The net NO3− fluxes and 15N content were decreased in zmga3ox plants under both LN and SN conditions. Exogenous GA3 could restore the NO3− uptake in zmga3ox plants, but uniconazole repressed NO3− uptake. Moreover, the transcript levels of ZmNRT2.1/2.2 were downregulated in zmga3ox plants, while the GA3 application enhanced the expression level. Furthermore, the RNA-seq analyses identified several transcription factors that are involved in the GA-mediated transcriptional operation of NRTs related genes. These findings revealed that GAs influenced N uptake involved in the transcriptional regulation of NRTs and physiological responses in maize responding to nitrogen supply.

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Use of growth retardants enables post-planting optimization of vegetative growth, which is particularly important with the ongoing climate change. Mepiquat chloride is an economical and safe retardant widely applied in cotton, but is not uniformly effective. Here identification of its molecular target as the ent-copalyl diphosphate synthase that initiates gibberellin biosynthesis enabled introduction of selective agrochemical inhibition, leaving intact more specialized metabolism important for resistance to biotic and abiotic stresses.