The physio-molecular responses of bread wheat (Triticum aestivum L.) induced by coexisting Phalaris minor Retz. under nitrate-limiting conditions: perspectives of kin and non-kin recognition

Abstract

The present study is aimed at understanding the physiological and molecular responses of a wheat genotype (K9107), induced by the presence of P. minor in its vicinity, on root system architecture (RSA), 15N uptake, and the gene expression of TaNPF6.4 in seminal and lateral roots under optimal and NO3−-limiting conditions. Seedlings of both species were grown in a vermiculite-perlite mixture for a defined period until they achieved comparable biomass at the earliest. Then 2D images of roots were analyzed. The Kjeldahl and Isotope Ratio Mass Spectroscopy methods were used to measure total N and δ15N in wheat tissues. The transcript expression of all homeologs of the TaNPF6.4 gene was studied by Real-Time-Polymerase Chain Reaction (qPCR) analysis. The upstream sequences of TaNPF6.4 were cloned in the pJET1.2 cloning vector, and Cis-Regulatory Elements were identified using the PLACE database. Root length and fresh and dry weight of roots invariably increased under N-limiting conditions, which was further increased when grown in the vicinity of P. minor. Total root size (TRS), main root path length (MRP), lateral root size (LRS), and first and second-order lateral root numbers (FOLRN and SOLRN) of wheat seedlings increased when they grew in the vicinity of P. minor, especially under the N-limiting (0.08 mM NO3−) condition. The wheat seedling had the lowest 15N-enrichment in P. minor association under NO3−-limiting condition than other conditions. We identified four closest sequences orthologous to AtNRT1.1, a dual affinity nitrate transceptor, located on chromosomes 4, 5, and 7 of three sub-genomes of wheat, known as TaNPF6.4. The homeolog-specific expression of TaNPF6.4 revealed that the gene encoded by sub-genome A is the highest expressing homeolog in both seminal and lateral roots with enhanced relative expression under N-limiting conditions when grown along with P. minor. The upstream Cis-Regulatory Elements of all these four homeologous genes showed considerable variation in numbers. Our study demonstrates the modulation in architecture and development of wheat roots, differential expression of TaNPF6.4, and adverse effect on N uptake in P. minor association more severely under nitrate-limiting conditions, indicating a possible role of TaNPF6.4 in perceiving nitrate under kin and non-kin association.