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

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), 15 N uptake, and the gene expression of TaNPF6.4 in seminal and lateral roots under optimal and NO 3 − -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 δ 15 N 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 NO 3 − ) condition. The wheat seedling had the lowest 15 N-enrichment in P. minor association under NO 3 − -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.