Maize (Zea mays L.) is a chilling-sensitive plant. Chilling stress in the early seedling stage seriously limits the growth, development, productivity and geographic distribution of maize. Salicylic acid (SA) is a plant growth regulator involved in the defenses against abiotic and biotic stresses as well as in plant development. However, the physiological mechanisms underlying the effects of foliar applied SA on different maize inbred lines under chilling stress are unclear. Two inbred lines, cold-sensitive cv. C546 and cold-tolerant cv. B125, were used to study the effects of SA on the growth and physiology of maize seedlings. The results showed that the application of SA at 50 mg/L on the leaves of maize seedlings under 4 °C decreased the relative electrolyte conductivity (REC) and the malondialdehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O_2⁻) content due to increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activity; SA also improved photosynthesis in the seedlings through increased chlorophyll content, enhanced Pn and Gs, and decreased Ci. SA application also increased the proline content and the relative water content (RWC) in the maize seedlings, thereby improving their osmotic adjustment capacity. The increase rate caused by SA of plant height and dry weight in C546 were 10.5% and 5.4% higher than that in B125 under 4 °C. In conclusion, SA promotes maize seedling growth and physiological characteristics, thus enhancing chilling resistance and the effect of SA on the chilling resistance of cold-sensitive cv. was stronger than that on cold-tolerant cv. at the low temperature.

Plant height is an important component of plant architecture, and significantly affects crop quality and yield. A soybean GmRAV (Related to ABI3/VP1) transcription factor containing both AP2 and B3 domains is a growth repressor. Three GmRAV-overexpressing (GmRAV-ox) transgenic lines displayed extremely shorter height and shortened internodes compared with control plants, whereas transgenic inhibition of GmRAV expression resulted in increased plant height. GmRAV-ox soybean plants showed a low active gibberellin level and the dwarf phenotype could be rescued by treatment with exogenous GA₃ treatment. ChIP (Chromatin immunoprecipitation)-qPCR assay showed that GmRAV could directly regulate the expression of the GA4 biosynthetic genes GA3-oxidase (GmGA3ox) by binding two CAACA motifs in the GmGA3ox promoter. The GmGA3ox promoter was bound by GmRAV, whose expression levels in leaves were both elevated in GmRAV-i-3 and decreased in GmRAV-ox-7 soybean plants. Transient expression assay in N. benthamiana also showed that the proGmRAV:GmRAV-3F6H effector strongly repressed the expression of LUC reporter gene driven by GmGA3ox promoter containing two CAACA motifs. Together, our results suggested that GmRAV protein repressed the expression of GmGA3ox by directly binding to the two CAACA motifs in the promoter to limit soybean plant height.

The RIQ gene can optimize the structure of light-harvesting complex II by regulating the degree of granum stacking, and ultimately participates in plant light stress responses. The GmRIQ2 gene contributes to plant photoprotection and may be involved in negative regulation of yield. To understand the regulatory mechanisms of GmRIQ2 expression, we isolated the GmRIQ2 promoter (PGmRIQ2) from the KenFeng 16 soybean genome. Sequence analysis showed that several cis-acting elements were involved in hormone responsiveness, seed-specific regulation, anaerobic induction and light responsiveness. PGmRIQ2 was expressed in soybean roots. GUS activity was detected in Arabidopsis thaliana rosette leaves, stems and roots, indicating that PGmRIQ2 tended to drive expression in rosette leaf vascular tissue and had spatiotemporal expression characteristics at the early growth stage. Three promoter deletion fragments of 450 bp, 284 bp and 194 bp were obtained by 5′ deletion. These three fragments all drove GUS gene expression in Arabidopsis thaliana rosette leaves, stems and roots. GUS gene expression decreased with deletion fragment truncation. In addition, the PGmRIQ2 auxin (IAA), abscisic acid (ABA) and methyl jasmonate (MeJA) response elements were located at base pairs −1661~−450, −450~−284 and −284~−194, respectively, and the promoter was induced by IAA, ABA, MeJA and light.