The phytohormone salicylic acid (SA) plays a crucial role in plant growth and development. However, the mechanism of high-concentration SA-affected gravitropic response in plant root growth and root hair development is still largely unclear. In this study, wild-type, pin2 mutant and various transgenic fluorescence marker lines of Arabidopsis thaliana were investigated to understand how root growth is affected by high SA treatment under gravitropic stress conditions. We found that exogenous SA application inhibited gravitropic root growth and root hair development in a dose-dependent manner. Further analyses using DIRECT REPEAT5 (DR5)-GFP, auxin sensor DII-VENUS, auxin efflux transporter PIN2-GFP, trans-Golgi network/early endosome (TGN/EE) clathrin-light-chain 2 (CLC2)-mCherry and prevacuolar compartment (PVC) (Rha1)-mCherry transgenic marker lines demonstrated that high SA treatment severely affected auxin accumulation, root-specific PIN2 distribution and PIN2 gene transcription and promoted the vacuolar degradation of PIN2, possibly independent of clathrin-mediated endocytic protein trafficking. Our findings proposed a new underlying mechanism of SA-affected gravitropic root growth and root hair development via the regulation of PIN2 gene transcription and PIN2 protein endocytosis in plants.

Nutrient antagonism typically refers to the fact that too high a concentration of one nutrient inhibits the absorption of another nutrient. In plants, Ca²⁺ (Calcium) and Mg²⁺ (Magnesium) are the two most abundant divalent cations, which are known to have antagonistic interactions. Hence, maintaining their homeostasis is crucial for plant growth and development. In this study, we showed that MTP10 (Metal Tolerance Protein 10) is an important regulator for maintaining homeostasis of Mg and Ca in Arabidopsis. The mtp10 mutant displayed severe growth retardation in the presence of excess Mg²⁺, to which the addition of Ca²⁺ was able to rescue the phenotype of mtp10 mutant. Additionally, the deficiency of Ca²⁺ in the culture medium accelerated the high-Mg sensitivity of the mtp10 mutant. The yeast complementation assay suggested that AtMTP10 had no Ca²⁺ transport activity. And the ICP-MS data further confirmed the antagonistic relationship between Ca²⁺ and Mg²⁺, with the addition of Ca²⁺ reducing the excessive accumulation of Mg²⁺ and high-Mg inhibiting the uptake of Ca²⁺. We conclude that the Arabidopsis MTP10 is essential for the regulation of Mg and Ca homeostasis.

Dicotyledonous plants form an apical hook structure in attempt to protect their young cotyledons from mechanical damage as they break out from the coarse soil. In agricultural production, farmers sometimes apply glucose to the soil to improve plant growth performance. Here, we found that the energy molecules, such as sucrose and glucose, play an essential role in the apical hook development. When sucrose and glucose were available, the apical hooks were able to be sustained longer compared to that grown in sugar-free conditions. And this phenomenon is dose-dependent. Several energy metabolisms pathways, such as oxidative phosphorylation and glycolysis, play highly important roles in the apical hook development. Furthermore, RNA-seq data showed that the genes involved in starch and sucrose metabolism were up-regulated in plants grown in sugar-free conditions compared to that grown in sugar-treated plants, while genes related to phenylpropanoid metabolism were down-regulated. Our study demonstrated the important role of energy metabolism during the apical hook development of Arabidopsisetiolated seedlings.