Zinc-finger transcription factors play central roles in plant growth, development and abiotic stress responses. PLATZ encodes a class of plant-specific zinc-finger transcription factor. However, biological functions or physiological mechanism controlled by PLATZ are currently limited. GhPLATZ1 transcripts were considerably up-regulated by NaCl, mannitol, abscisic acid (ABA) and gibberellin (GA) treatments. Transgenic Arabidopsis by ectopic expression of GhPLATZ1 exhibited faster seed germination and higher seedling establishment under salt and mannitol stresses than those of wild type (WT), indicating enhanced osmotic insensitivity in GhPLATZ1 transgenic Arabidopsis. The ABA content in dry seeds of GhPLATZ1 transgenic Arabidopsis was lower than that of WT whereas the ABA content was not changed in germinating seeds under salt stress. Seed germination was faster than but the seedling establishment of transgenic Arabidopsis was similar to WT. Besides, GhPLATZ1 transgenic and WT Arabidopsis exhibited insensitivity to paclobutrazol (PAC), a GA biosynthesis inhibitor, whereas exogenous GA could eliminate the growth difference between GhPLATZ1 transgenic and WT Arabidopsis under salt stress. Moreover, exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), an ethylene precursor, exerted similar effects to GA. Furthermore, ABI4 and ETO1 transcripts were significantly down-regulated, whereas ACS8 was up-regulated in GhPLATZ1 transgenic Arabidopsis under salt stress. In conclusion, GhPLATZ1 had broad influence in responses to salt and mannitol stresses in transgenic Arabidopsis during seed germination and seedling establishment. The effect of GhPLATZ1 expression in transgenic Arabidopsis might be mediated by the ABA, GA, and ethylene pathways. Thus, this study provided new insights into the regulatory network in response to abiotic stresses in plants.

Summary: Genetic transformation is a critical tool for gene editing and genetic improvement of plants. Although many model plants and crops can be genetically manipulated, genetic transformation systems for fruit trees are either lacking or perform poorly. We used Rhizobium rhizogenes to transfer the target gene into the hairy roots of Malus domestica and Actinidia chinensis. Transgenic roots were generated within 3 weeks, with a transgenic efficiency of 78.8%. Root to shoot conversion of transgenic hairy roots was achieved within 11 weeks, with a regeneration efficiency of 3.3%. Finally, the regulatory genes involved in stem cell activity were used to improve shoot regeneration efficiency. MdWOX5 exhibited the most significant effects, as it led to an improved regeneration efficiency of 20.6% and a reduced regeneration time of 9 weeks. Phenotypes of the overexpression of RUBY system mediated red roots and overexpression of MdRGF5 mediated longer root hairs were observed within 3 weeks, suggesting that the method can be used to quickly screen genes that influence root phenotype scores through root performance, such as root colour, root hair, and lateral root. Obtaining whole plants of the RUBY system and MdRGF5 overexpression lines highlights the convenience of this technology for studying gene functions in whole plants. Overall, we developed an optimized method to improve the transformation efficiency and stability of transformants in fruit trees.