No abstract

Most terrestrial plants form a root symbiosis with arbuscular mycorrhizal (AM) fungi, which receive fixed carbon from the plant and enhance the plant's uptake of mineral nutrients. AM symbiosis improves the phosphorous and nitrogen nutrition of host plants; however, little is known about the role of AM symbiosis in potassium (K + ) nutrition. Here, we report that inoculation with the AM fungus Rhizophagus irregularis improved tomato (Solanum lycopersicum) plant growth and K + acquisition and that K + deficiency has a negative effect on root growth and AM colonization. Based on its homology to a Lotus japonicus AM-induced K + transporter, we identified a mycorrhiza-specific tomato K + transporter, SlHAK10 (Solanum lycopersicum High-affinity Potassium Transporter10), that was exclusively expressed in arbuscule-containing cells. SlHAK10 could restore a yeast K + uptake-defective mutant in the low-affinity concentration range. Loss of function of SlHAK10 led to a significant decrease in mycorrhizal K + uptake and AM colonization rate under low-K + conditions but did not affect arbuscule development. Overexpressing SlHAK10 from the constitutive cauliflower mosaic virus 35S promoter or the AM-specific Solanum melongena Phosphate Transporter4 not only improved plant growth and K + uptake but also increased AM colonization efficiency and soluble sugar content in roots supplied with low K + . Our results indicate that tomato plants have a SlHAK10-mediated mycorrhizal K + uptake pathway and that improved plant K + nutrition could increase carbohydrate accumulation in roots, which facilitates AM fungal colonization.

In recent decades, many new and exciting findings have paved the way to the better understanding of plant responses in various environmental changes. Some major areas are focused on role of phytohormone during abiotic stresses. Salicylic acid (SA) is one such plant hormone that has been implicated in processes not limited to plant growth, development, and responses to environmental stress. This review summarizes the various roles and functions of SA in mitigating abiotic stresses to plants, including heating, chilling, salinity, metal toxicity, drought, ultraviolet radiation, etc. Consistent with its critical roles in plant abiotic tolerance, this review identifies the gaps in the literature with regard to the complex signalling network between SA and reactive oxygen species, ABA, Ca2+, and nitric oxide. Furthermore, the molecular mechanisms underlying signalling networks that control development and stress responses in plants and underscore prospects for future research on SA concerning abiotic-stressed plants are also discussed.

Most land plants can form symbiosis with arbuscular mycorrhizal (AM) fungi to enhance uptake of mineral nutrients, particularly phosphate (Pi) and nitrogen (N), from the soil. It is established that transport of Pi from interfacial apoplast into plant cells depends on the H+ gradient generated by the H+‐ATPase located on the periarbuscular membrane (PAM); however, little evidence regarding the potential link between mycorrhizal N transport and H+‐ATPase activity is available to date. Here, we report that a PAM‐localized tomato H+‐ATPase, SlHA8, is indispensable for arbuscule development and mycorrhizal P and N uptake. Knockout of SlHA8 resulted in truncated arbuscule morphology, reduced shoot P and N accumulation, and decreased H+‐ATPase activity and acidification of apoplastic spaces in arbusculated cells. Overexpression of SlHA8 in tomato promoted both P and N uptake, and increased total colonization level, but did not affect arbuscule morphology. Heterogeneous expression of SlHA8 in the rice osha1 mutant could fully complement its defects in arbuscule development and mycorrhizal P and N uptake. Our results propose a pivotal role of the SlHA8 in energizing both the symbiotic P and N transport, and highlight the evolutionary conservation of the AM‐specific H+‐ATPase orthologs in maintaining AM symbiosis across different mycorrhizal plant species.