*4.1. Unique DEGs in the Low-N-Tolerant Genotype*

In 750-1, the unique DEGs involved in primary metabolism, secondary metabolism, stress response, and disease resistances were down-regulated in the leaves after long-term N deficiency. However, the relative biomass of 750-1 was significantly higher than that of the other cultivars (Table S2), indicating that the growth of 750-1 was repressed less than other cultivars under N starvation. The relative values of root dry weights and leaf areas of 750-1 were much higher than those of other cultivars (Table S2), implying a larger absorption area of N and stronger photosynthesis in 750-1. Interestingly, genes of *somatic embryogenesis receptor kinase 2 (SERK2)-like* (*LOC107857123*) and *LRR receptorlike serine/threonine-protein kinase* (*LOC107869144* and *LOC107869171*) were up-regulated in the leaves of 750-1 (Figure 7G). Both SERK2 and LRR receptor-like serine/threonineprotein kinase belong to the receptor-like kinase (RLK) family. SERK2 is essential for male microsporogenesis in *Arabidopsis* [40]. It has been postulated that at an early low-N stress stage, processes such as absorption, transportation, and assimilation of N might be highly enhanced in 750-1 under low-N conditions, as well as primary metabolism, which could result in improved biomass accumulation in 750-1 relative to other cultivars. After longterm N limitation, 750-1 might slowly decrease vegetative growth and enter reproductive stage earlier to accelerate its life cycle and seed handing down.
