Plant growth and development are closely related to phosphate (Pi) and auxin. However, data regarding auxin response factors (ARFs) and their response to phosphate in maize are limited. Here, we isolated ZmARF4 in maize and dissected its biological function response to Pi stress. Overexpression of ZmARF4 in Arabidopsis confers tolerance of Pi deficiency with better root morphology than wild-type. Overexpressed ZmARF4 can partially restore the absence of lateral roots in mutant arf7 arf19. The ZmARF4 overexpression promoted Pi remobilization and up-regulated AtRNS1, under Pi limitation while it down-regulated the expression of the anthocyanin biosynthesis genes AtDFR and AtANS. A continuous detection revealed higher activity of promoter in the Pi-tolerant maize P178 line than in the sensitive 9782 line under low-Pi conditions. Meanwhile, GUS activity was specifically detected in new leaves and the stele of roots in transgenic offspring. ZmARF4 was localized to the nucleus and cytoplasm of the mesophyll protoplast and interacted with ZmILL4 and ZmChc5, which mediate lateral root initiation and defense response, respectively. ZmARF4 overexpression also conferred salinity and osmotic stress tolerance in Arabidopsis. Overall, our findings suggest that ZmARF4, a pleiotropic gene, modulates multiple stress signaling pathways, and thus, could be a candidate gene for engineering plants with multiple stress adaptation.

Phosphorus (P) deficiency is one of the most critical factors for plant growth and productivity, including its inhibition of lateral root initiation. Auxin response factors (ARFs) play crucial roles in root development via auxin signaling mediated by genetic pathways. In this study, we found that the transcription factor ZmARF1 was associated with low inorganic phosphate (Pi) stress-related traits in maize. This superior root morphology and greater phosphate stress tolerance could be ascribed to the overexpression of ZmARF1. The knock out mutant zmarf1 had shorter primary roots, fewer root tip number, and lower root volume and surface area. Transcriptomic data indicate that ZmLBD1, a direct downstream target gene, is involved in lateral root development, which enhances phosphate starvation tolerance. A transcriptional activation assay revealed that ZmARF1 specifically binds to the GC-box motif in the promoter of ZmLBD1 and activates its expression. Moreover, ZmARF1 positively regulates the expression of ZmPHR1, ZmPHT1;2, and ZmPHO2, which are key transporters of Pi in maize. We propose that ZmARF1 promotes the transcription of ZmLBD1 to modulate lateral root development and Pi-starvation induced (PSI) genes to regulate phosphate mobilization and homeostasis under phosphorus starvation. In addition, ZmERF2 specifically binds to the ABRE motif of the promoter of ZmARF1 and represses its expression. Collectively, the findings of this study revealed that ZmARF1 is a pivotal factor that modulates root development and confers low-Pi stress tolerance through the transcriptional regulation of the biological function of ZmLBD1 and the expression of key Pi transport proteins.

Photoperiod sensitivity poses a major obstacle to the expansion, breeding, and production of maize (Zea mays) in temperate regions. While the photoperiod-dependent FLOWERING LOCUS T (FT)/ZCNs pathway modulates floral development, the mechanism by which crops perceive specific light wavelengths and regulate flowering remains largely unknown. In this study, we demonstrate that the rhythmic expression of the blue light receptor FLAVIN-BINDING KELCH REPEAT F-BOX 1a (ZmFKF1a) is finely controlled by the Evening Complex (EC) components of LUX ARRHYTHMO 2 (ZmLUX2). ZmFKF1a interacts with GIGANTEA 1 (ZmGI1), stabilizing it and promoting its nuclear localization via a blue light-dependent mechanism. In the nucleus, ZmGI1 directly binds and activates Zea mays MADS-box 4 (ZMM4), a MADS-box gene specifically expressed in the shoot apical meristem, which drives floral transition. Genetic analyses revealed that ZmGI1 is epistatic to ZmFKF1a in promoting shoot apex development and accelerating flowering in maize. Our findings elucidate a ZmLUX2-ZmFKF1a–ZmGI1-ZMM4 regulatory module that fine-tunes photoperiodic flowering of day-neutral temperate maize lines, functioning independently of ZEA CENTRORADIALISs (ZCNs). Furthermore, transgenic maize overexpressing ZmFKF1a exhibited accelerated flowering and enhanced yield specifically in photoperiod-sensitive tropical maize lines under extreme natural long-day conditions, underscoring its potential application in improving maize production through precise manipulation of flowering traits. These insights advance our understanding of how blue light signaling orchestrates flowering time in maize and offer a promising strategy for optimizing crop performance in diverse environments.