Approaches for enhancement of N₂ fixation efficiency of chickpea (Cicer arietinum L.) under limiting nitrogen conditions

Abstract

SummaryChickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N 2 inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar 'Bivanij' as well as studied the mechanism underlying the improvement of N 2 fixation efficiency. Our data revealed that C-15 strain manifested the most efficient N 2 fixation in comparison with Ch-191 or CP-36. This finding was supported by higher plant productivity and expression levels of the nifHDK genes in C-15 nodules. Nodule specific activity was significantly higher in C-15 combination, partially as a result of higher electron allocation to N 2 versus H + . Interestingly, a striking difference in nodule carbon and nitrogen composition was observed. Sucrose cleavage enzymes displayed comparatively lower activity in nodules established by either Ch-191 or CP-36. Organic acid formation, particularly that of malate, was remarkably higher in nodules induced by C-15 strain. As a result, the best symbiotic efficiency observed with C-15-induced nodules was reflected in a higher concentration of the total and several major amino metabolites, namely asparagine, glutamine, glutamate and aspartate. Collectively, our findings demonstrated that the improved efficiency in chickpea symbiotic system, established with C-15, was associated with the enhanced capacity of organic acid formation and the activities of the key enzymes connected to the nodule carbon and nitrogen metabolism.

Adaptation of the symbiotic Mesorhizobium –chickpea relationship to phosphate deficiency relies on reprogramming of whole-plant metabolism

“…Previous reports have suggested that expression levels of nifD and nifK genes could be used as indicators of SNF capacity (9,(16)(17)(18). The higher levels of nifD and nifK expression under Pisufficient conditions observed in MmSWRI9-induced nodules relative to McCP-31-induced nodules suggest that the MmSWRI9-inoculated association may have higher SNF capacity than the McCP-31-inoculated association under Pi-sufficient conditions (Fig.…”

“…SNF capability of leguminous plants is controlled by the rhizobial nitrogenase complex, which catalyzes the reduction of N 2 into ammonia (15). The nifDK genes are the structural genes encoding the MoFe protein subunits of the nitrogenase complex, and assessing their expression levels has been shown to be a reliable method for evaluating the contribution of the N 2 fixing bacteria to plant N nutrition (9,(16)(17)(18). Thus, analysis of the expression levels of the nifDK genes will enable us to characterize the SNF capacity of the nodules induced by the tested strains under both normal and low Pi conditions (Fig.…”

“…Chickpea genome annotation (Bioproject PRJNA175619) and key genes identified as Pi starvation response-related genes in Arabidopsis were used in a search for putative Pi starvation response-related genes in chickpea (19,23,(52)(53)(54)(55). The identified chickpea genes and the specific primers used to amplify these genes using real-time quantitative RT-PCR (qRT-PCR) are listed in Dataset S5; 16S rRNA (NR_025953) (9) and IF4a (XM_004513380) (56) were used as reference genes for expression analysis of the nifDK and selected Pi starvation response-related chickpea genes. Analyses of the qRT-PCR data were performed as previously described (57).…”

“…Leaf, root, and nodule samples of four biological replicates were extracted as previously described (9). Total soluble protein content was estimated using the Bradford reagent (58).…”

“…Being one of the major pulse crops in the world, chickpea (Cicer arietinum L.) is traditionally cultivated in many countries of different continents (9). It ranks third globally in total yield among grain legume crops (10).…”