Knockdown of OsSAE1a affects acquisition and mobilization of nitrogen, and growth and development of rice

Sumoylation, ubiquitination, and phosphorylation are pivotal post-translational modifications that play key roles in regulating the homeostasis of nitrogen (N). Sumoylation comprises conjugation/deconjugation of Small Ubiquitin-like Modifier (SUMO) proteins to other proteins thereby modifying their functions. The first step in SUMO conjugation is catalyzed by the heterodimeric E1 activating enzyme. It comprises small SAE1 and large SAE2 subunits, which are encoded by three (SAE1a, SAE1b1, and SAE1b2) and one (SAE2) gene, respectively in Arabidopsis. OsSAE1a is the ortholog of Arabidopsis in rice. Here, the role of OsSAE1a in the acquisition and mobilization of N, and its influence on the growth and development of rice was investigated. The qRT-PCR assay revealed a significant increase in the relative expression level of OsSAE1a in the roots of the seedlings grown hydroponically under LN condition (0 mM NH4NO3) compared with the roots of the seedlings grown under NN (1.25 mM NH4NO3) condition for 1 day. Further, the reverse genetics approach was used by generating rice transgenic lines with RNAi-mediated knockdown of OsSAE1a. Although there was an increase in the influx of 15N-NH4+, the root/shoot ratio of RNAi lines reduced compared with the wild-type during N deficiency. N deficiency also triggered up-regulation of some of the genes (OsAMT1;2, OsAMT1;3, OsNRT2.1, OsNRT2.2, OsNRT2.3a, OsNRT2.4, and OsNAR2.2) in RNAi lines that are implicated in regulating the acquisition and/or mobilization of N. Further, RNAi lines also exhibited adverse effects on several traits (panicle length, per cent seed set, and total N concentration in the lower leaf blade) during growth to the maturity in a potting mix. The study thus highlighted the regulatory influences of OsSAE1a on the acquisition and mobilization of N, and some of the traits governing growth and development.