Chenopodium quinoa Willd (quinoa), a member of the Amaranthaceae family, is an allotetraploid annual plant, endemic to South America. The plant of C. quinoa presents significant ecological plasticity with exceptional adaptability to several environmental stresses, including salinity. The resilience of quinoa to several abiotic stresses, as well as its nutritional attributes have led to significant shifts in quinoa cultivation worldwide over the past century. This work first defines germination sensu stricto in quinoa where the breakage of the pericarp and the testa is followed by endosperm rupture (ER). Transcriptomic changes in early seed germination stages lead to unstable expression levels in commonly used reference genes that are typically stable in vegetative tissues. Noteworthy, no suitable reference genes have been previously identified specifically for quinoa seed germination under salt stress conditions. This work aims to identify these genes as a prerequisite step for normalizing qPCR data. To this end, germinating seeds from UDEC2 and UDEC4 accessions, with different tolerance to salt, have been analyzed under conditions of absence (0 mM NaCl) and in the presence (250 mM NaCl) of sodium chloride. Based on relevant literature, six candidate reference genes: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Monensin sensitivity1 (MON1), Polypyrimidine tract-binding protein (PTBP), Actin-7 (ACT7), Ubiquitin-conjugating enzyme (UBC), and 18S ribosomal RNA (18S), were selected and assessed for stability using the RefFinder Tool encompassing the statistical algorithms geNorm, NormFinder, BestKeeper, and ΔCt in the evaluation. The data presented supports the suitability of CqACT7 and CqUBC as reference genes for normalizing gene expression during seed germination under salinity stress. These recommended reference genes can be valuable tools for consistent qPCR studies in quinoa seeds.

The root-colonizing endophytic fungus Piriformospora indica promotes root and shoot growth of its host plants. We show that growth promotion of Arabidopsis leaves is abolished when the seedlings are grown on media with nitrogen (N) limitation. The fungus neither stimulated the total N content nor did it promote 15NO3- uptake from agar plates to the leaves of the host under N-sufficient or N-limiting conditions. However, when the roots were co-cultivated with 15N-labelled P. indica, more label can be detected in the leaves of N-starved host plants, but not of plants supplied with sufficient N. Amino acid and primary metabolite profiles, as well as expression analyses of N metabolite transporter genes suggest that the fungus alleviates the adaptation of its host to the N limitation condition. P. indica alters the expression of transporter genes which participate in relocation of NO3-, NH4+ and N metabolites from the roots to the leaves under N limitation. We propose that P. indica participates in the plant´s metabolomic adaptation to N limitation by delivering reduced N metabolites to the host, alleviating metabolic N starvation responses, and reprogramming the expression of N-metabolism related genes.