Silencing of SlSPX1 and SlSPX2 promote growth and root mycorrhization in tomato (Solanum lycopersicum L.) seedlings.

Owing to the essential requirement of phosphorus (P) for growth and development, plants tightly control inorganic phosphate (Pi) homeostasis. SPX-PHR regulatory circuit not only control phosphate homeostasis responses but also root mycorrhization by arbuscular mycorrhiza (AM) fungi. Besides sensing Pi deficiency, SPX (SYG1/Pho81/XPR1) proteins also control the transcription of P starvation inducible (PSI) genes by blocking the activity of PHR1 (PHOSPHATE STARVATION RESPONSE1) homologs in plants under Pi-sufficient conditions. However, the roles of SPX members in Pi homeostasis and AM fungi colonization remain to be fully recognized in tomato. In this study, we identified 17 SPX-domain containing members in the tomato genome. Transcript profiling revealed the high Pi-specific nature of their activation. Four SlSPX members have also induced in AM colonized roots. Interestingly, we found that SlSPX1 and SlSPX2 are induced by P starvation and AM fungi colonization. Further, SlSPX1 and SlSPX2 exhibited varying degrees of interaction with the PHR homologs in this study. Virus-induced gene silencing-based (VIGS) transcript inhibition of these genes alone or together promoted the accumulation of higher total soluble Pi in tomato seedlings and improved their growth. It also enhanced AM fungi colonization in the roots of SlSPX1 and SlSPX2 silenced seedlings. Overall, the present study provides evidence in support of SlSPX members being good candidates for improving AM fungi colonization potential in tomato.

Cryo-milled nano-DAP for enhanced growth of monocot and dicot plants.

Phosphorus (P) is a limiting macronutrient that regulates plant growth and development based on the bioavailability of its inorganic form, i.e., orthophosphate (Pi). P plays a critical role in cell development, and it is a key component of ATP, DNA, lipids, and cell signaling machinery. Without the exogenous application of P fertilizers, the yield of crops will not meet the ever-growing demand in today's world. However, due to the non-renewable nature of natural P reserves and simultaneous rapid human population growth, food crops must be ultimately produced more than ever by using a lower P fertilizer input. Hence, the strategy of preparing nano-fertilizers was conceptualized and demonstrated with great success. For example, nano-diammonium phosphate (n-DAP) performed far better than the commercial granular DAP (c-DAP). However, nano-fertilizers, including n-DAP, cannot be produced on a large scale using the available processing methods. Herein, a novel processing strategy, namely cryo-milling, is demonstrated to prepare n-DAP on a kg-scale without altering DAP's bonding structure. Cryo-milling involves milling at liquid N2 temperatures and therefore helps in brittle fracture of coarser DAP particles into n-DAP particles. Cryo-milled n-DAP, with particle size ∼5000 times smaller but specific surface area ∼14 000 times greater than that of c-DAP, enhanced the growth of monocot (wheat) and dicot (tomato) plants due to improved bioavailability of Pi even for a far lower input than c-DAP. Phenotypic observations such as higher leaf biomass, longer shoots, shorter roots, and less anthocyanin pigmentation manifested the extraordinary efficacy of cryo-milled n-DAP for 75% lower input than c-DAP.