Summary: Plant genetic transformation is a crucial step for applying biotechnology such as genome editing to basic and applied plant science research. Its success primarily relies on the efficiency of gene delivery into plant cells and the ability to regenerate transgenic plants. In this study, we have examined the effect of several developmental regulators (DRs), including PLETHORA (PLT5), WOUND INDUCED DEDIFFERENTIATION 1 (WIND1), ENHANCED SHOOT REGENERATION (ESR1), WUSHEL (WUS) and a fusion of WUS and BABY‐BOOM (WUS‐P2A‐BBM), on in planta transformation through injection of Agrobacterium tumefaciens in snapdragons (Antirrhinum majus). The results showed that PLT5, WIND1 and WUS promoted in planta transformation of snapdragons. An additional test of these three DRs on tomato (Solanum lycopersicum) further demonstrated that the highest in planta transformation efficiency was observed from PLT5. PLT5 promoted calli formation and regeneration of transformed shoots at the wound positions of aerial stems, and the transgene was stably inherited to the next generation in snapdragons. Additionally, PLT5 significantly improved the shoot regeneration and transformation in two Brassica cabbage varieties (Brassica rapa) and promoted the formation of transgenic calli and somatic embryos in sweet pepper (Capsicum annum) through in vitro tissue culture. Despite some morphological alternations, viable seeds were produced from the transgenic Bok choy and snapdragons. Our results have demonstrated that manipulation of PLT5 could be an effective approach for improving in planta and in vitro transformation efficiency, and such a transformation system could be used to facilitate the application of genome editing or other plant biotechnology application in modern agriculture.

Seed germination is a critical developmental phase for seedling establishment and crop production. Increasing salinity stress associated with climatic change can pose a challenge for seed germination and stand establishment of many crops including lettuce. Here, we show that water soluble carbon nanoparticles (CNPs) can significantly promote seed germination without affecting seedling growth. Twenty-seven varieties of lettuce (Lactuca sativa) were screened for sensitivity to germination in 150 and 200 mM NaCl, and six salt-sensitive varieties (Little Gem, Parris Island, Breen, Butter Crunch, Muir, and Jericho) were selected and primed with 0.3% soluble carbon nanoparticles. Pretreatment with CNPs significantly improved seed germination under 150 mM NaCl and high temperature. CNP treatment slightly inhibited the elongation of primary roots but promoted lateral root growth and accumulation of chlorophyll content of seedlings grown under salt stress. Despite different lettuce varieties exhibiting a distinct response to nanoparticle treatments, results from this study indicate that soluble nanoparticles can significantly improve lettuce seed germination under salinity stress, which provide fundamental evidence on the potential of nanoparticles in agricultural application to improve crop yield and quality under stressful conditions.

Silicon has been proven to exert beneficial effects on plant growth and stress tolerance, and silicon accumulation varies among different plant species. Cucumber (Cucumis sativus) is a widely used dicot model for silicon accumulation, but little is known about the molecular mechanism of its silicon uptake. Previously, we isolated and characterized CsLsi1, a silicon influx transporter gene from cucumber. In this study, we cloned a putative silicon efflux transporter gene, CsLsi2, from cucumber and investigated its role in silicon uptake. The expression pattern, transport activity, and subcellular and cellular localizations of CsLsi2 were investigated. The transport activity of CsLsi2 was determined in Xenopus laevis oocytes. The subcelluar and cellular localizations were conducted by transient expression of fused 35S::CsLsi2-eGFP in onion epidermal cells and expression of ProCsLsi2::CsLsi2-mGFP in cucumber, respectively. CsLsi2 was mainly expressed in the roots. Expression of CsLsi2-eGFP fusion sequence in onion epidermis cells showed that CsLsi2 was localized at the plasma membrane. Transient expression in Xenopus laevis oocytes showed that CsLsi2 demonstrated efflux but no influx transport activity for silicon, and the transport was energy-dependent. Expression of CsLsi2-mGFP under its own promoter revealed that CsLsi2 was mainly expressed on endodermal cells, showing no polar distribution. In combination with our previous work on CsLsi1, a model for silicon uptake in cucumber roots is proposed. The results suggest that CsLsi2 is a silicon efflux transporter gene in cucumber. The coordination of CsLsi1 and CsLsi2 mediates silicon uptake in cucumber roots. This study may help us understand the molecular mechanism for silicon uptake in cucumber, one of the few dicots with a relatively high capacity for silicon accumulation.

Seed germination and seedling vigor can be affected by environmental cues experienced by the mother plant. However, information about how the maternal environment affects seed quality is scarce in ornamental plants. This study aimed to investigate the effects of two different maternal environments on the seed germination and seedling vigor of Petunia × hybrida under a variety of abiotic stresses. Petunia mother plants were grown in either a greenhouse during the summer months or an indoor controlled-temperature-and-light environment. Collected seeds were subjected to external stressors, including polyethylene glycol (PEG), sodium chloride (NaCl), high temperature, and abscisic acid (ABA), to determine seed germination percentage and seedling vigor. Results indicated that seeds harvested from the mother plants grown in a controlled environment germinated better than seeds harvested from the mother plants grown in the greenhouse when suboptimal germination conditions were applied. Additionally, the seedlings from the controlled maternal environment performed better in both ABA and salinity stress tests than the greenhouse seedlings. Interestingly, the greenhouse seedlings displayed less reactive oxygen species (ROS) damage and lower electrolyte leakage than the controlled environment seedlings under dehydration stress. The difference in germination and seedling vigor of seeds from the two different maternal environments might be due to the epigenetic memory inherited from the mother plants. This study highlighted the strong impact of the maternal environment on seed germination and seedling vigor in Petunia and may assist in high-quality seed production in ornamental plants.

Some chloroplast proteins are known to serve as messengers to transmit retrograde signals from chloroplasts to the nuclei in response to environmental stresses. However, whether particular chloroplast proteins respond to drought stress and serve as messengers for retrograde signal transduction are unclear. Here, we used isobaric tags for relative and absolute quantitation (iTRAQ) to monitor the proteomic changes in tobacco (Nicotiana benthamiana) treated with drought stress/re-watering. We identified 3936 and 1087 differentially accumulated total leaf and chloroplast proteins, respectively, which were grouped into 16 categories. Among these, one particular category of proteins, that includes carbonic anhydrase 1 (CA1), exhibited a great decline in chloroplasts, but a remarkable increase in leaves under drought stress. The subcellular localizations of CA1 proteins from moss (Physcomitrella patens), Arabidopsis thaliana and rice (Oryza sativa) in P. patens protoplasts consistently showed that CA1 proteins gradually diminished within chloroplasts but increasingly accumulated in the cytosol under osmotic stress treatment, suggesting that they could be translocated from chloroplasts to the cytosol and act as a signal messenger from the chloroplast. Our results thus highlight the potential importance of chloroplast proteins in retrograde signaling pathways and provide a set of candidate proteins for further research.