The Role of Multifunctional RNA Binding Protein Os Tudor‐SN in Affecting Storage Protein RNA Transport and Seed Morphology in Rice

The major storage proteins of rice, prolamines and glutelins, are synthesized and packaged in the ER lumen and vacuole, respectively. The sorting of these storage proteins into different endomembrane compartments is facilitated by the localization of these RNAs to distinct ER subdomains. A prominent player in RNA localization in rice is Tudor‐SN, a highly conserved RNA binding protein that is well documented to play multiple nuclear and cytoplasmic roles in eukaryotic cells. We hypothesize that Tudor‐SN's multi‐functional properties are due to its modular domain structure consisting of four SN domains, Tudor domain and partial SN domain, where individual domains are responsible for specific processes in gene regulation and RNAs transport. To provide evidence for this view, two TILLING (Targeted Induced Local Lesions in Genomes) mutant lines, EM1084 and PMT64, which have mutations in the third SN and Tudor domains, respectively were identified. Compared to wild type, these mutant lines grow slower and exhibit considerable differences in grain weight and appearance. In situ RT‐PCR showed that RNA localization profile are altered in these mutant lines. PMT64 showed mis‐localization of prolamine RNAs to the cisternal‐ER whereas the targeting of glutelin RNAs was unaffected. EM1084 also showed a similar disruption in prolamine RNAs localization but also exhibited partial mis‐localization of glutelin RNAs to the PB‐ER. These significant differences in RNA localization mediated by mutations in the SN3 domain and Tudor domain, respectively, indicate that different domains of Os Tudor‐SN are involved in distinct molecular processes.