Phosphorus is the second most critical macronutrient after nitrogen required for metabolism, growth, and development of plants. Despite the abundance of phosphorus in both organic and inorganic forms in the soil, it is mostly unavailable for plant uptake due to its complexation with metal ions in the soil. The use of agrochemicals to satisfy the demand for phosphorus to improve crop yield has led to the deterioration of the ecosystem and soil health, as well as an imbalance in the soil microbiota. Consequently, there is a demand for an alternate cost-effective and eco-friendly strategy for the biofortification of phosphorus. One such strategy is the application of phosphate-solubilizing microorganisms which can solubilize insoluble phosphates in soil by different mechanisms like secretion of organic acids, enzyme production, and excretion of siderophores that can chelate the metal ions and form complexes, making phosphates available for plant uptake. These microbes not only solubilize phosphates but also promote plant growth and crop yield by producing plant-growth-promoting hormones like auxins, gibberellins, and cytokinins, antibiosis against pathogens, 1-aminocyclopropane-1-carboxylic acid deaminase which enhances plant growth under stress conditions, improving plant resistance to heavy metal toxicity, and so on. Pyrroloquinoline quinine (pqq) and glucose dehydrogenase (gcd) are the representative genes for phosphorus solubilization in microorganisms. The content presented in this review paper focuses on different mechanisms and modes of action of phosphate-solubilizing microorganisms, their contribution to phosphorus solubilization, growth-promoting attributes in plants, and the molecular aspects of phosphorus solubilization.

Availability of Zn to plant is hampered by its immobile nature and adverse soil conditions. Thus, Zn deficiency is observed even though high amount is available in soil. Root-shoot barrier, a major controller of zinc transport in plant is highly affected by changes in the anatomical structure of conducting tissue and adverse soil conditions like pH, clay content, calcium carbonate content, etc. Zn deficiency results in severe yield losses and in acute cases plant death. Zn deficiency in edible plant parts results in micronutrient malnutrition leading to stunted growth and improper sexual development in humans. To overcome this problem several strategies have been used to enrich Zn availability in edible plant parts, including nutrient management, biotechnological tools, and classical and molecular breeding approaches.

Rice is inherently low in micronutrients, especially iron, which leads to severe malnutrition problems in rice-consuming populations. Different plant growth promoting rhizobacterial strains (PGPRs) (viz. Pseudomonas putida, Pseudomonas fluorescens, and Azospirillum lipoferum from a microbial collection and B 15, B 17, B 19, BN 17 and BN 30 isolated from the rhizospheric soils) were applied to field grown rice plants with an aim to increase the iron content of grains. 16S rRNA gene sequence showed that isolates belong to Enterobacteria species. Different parameters related to the increase in iron content of plants show an enhancement upon treatment of rice plants with PGPRs. Treatments with P. putida, B 17 and B 19 almost doubled the grain iron content. Besides this, the translocation efficiency of the iron from roots to shoots to grains was also enhanced upon treatment with PGPRs. It is therefore concluded that application of PGPR strains is an important strategy to combat the problem of iron deficiency in rice and consecutively in human masses.

Plant growth promoting rhizobacteria (PGPRs) improve growth of the host plants in a variety of ways. For this reason five bacterial strains isolated form the rice rhizospheric soil (B 15, B 17, B 19, BN 17 and BN 30) and three standard PGPR strains (viz. Pseudomonas putida, Pseudomonas fluorescens and Azospirillum lipoferum) were tested for plant growth promotion when applied to the rice plants as seedling treatments. The experiment was conducted for two rainy seasons of the years 2010 and 2011. Rice plants inoculated with the bacterial isolates recorded an improved plant growth and higher photosynthetic capacity signified by the higher chlorophyll content. Root and shoot dry mass was also found to be increased in the inoculated plants. Besides these iron and zinc content of the treated rice plants was also found to be higher in comparison with the uninoculated control plants. Hence, it can be concluded that application of PGPR has immense potential to be used as agricultural crop inoculants as they promote plant growth as well as improve the health and yield of the plants.

BackgroundIn finger millet, calcium is one of the important and abundant mineral elements. The molecular mechanisms involved in calcium accumulation in plants remains poorly understood. Transcriptome sequencing of genetically diverse genotypes of finger millet differing in grain calcium content will help in understanding the trait.Principal FindingIn this study, the transcriptome sequencing of spike tissues of two genotypes of finger millet differing in their grain calcium content, were performed for the first time. Out of 109,218 contigs, 78 contigs in case of GP-1 (Low Ca genotype) and out of 120,130 contigs 76 contigs in case of GP-45 (High Ca genotype), were identified as calcium sensor genes. Through in silico analysis all 82 unique calcium sensor genes were classified into eight calcium sensor gene family viz., CaM & CaMLs, CBLs, CIPKs, CRKs, PEPRKs, CDPKs, CaMKs and CCaMK. Out of 82 genes, 12 were found diverse from the rice orthologs. The differential expression analysis on the basis of FPKM value resulted in 24 genes highly expressed in GP-45 and 11 genes highly expressed in GP-1. Ten of the 35 differentially expressed genes could be assigned to three documented pathways involved mainly in stress responses. Furthermore, validation of selected calcium sensor responder genes was also performed by qPCR, in developing spikes of both genotypes grown on different concentration of exogenous calcium.ConclusionThrough de novo transcriptome data assembly and analysis, we reported the comprehensive identification and functional characterization of calcium sensor gene family. The calcium sensor gene family identified and characterized in this study will facilitate in understanding the molecular basis of calcium accumulation and development of calcium biofortified crops. Moreover, this study also supported that identification and characterization of gene family through Illumina paired-end sequencing is a potential tool for generating the genomic information of gene family in non-model species.