Transcription factor OsSHR2 regulates rice architecture and yield per plant in response to nitrogen.

MAIN CONCLUSION: Mutation of OsSHR2 adversely impacted root and shoot growth and impaired plant response to N conditions, further reducing the yield per plant. Nitrogen (N) is a crucial factor that regulates the plant architecture. There is still a lack of research on it. In our study, it was observed that the knockout of the SHORTROOT 2 (OsSHR2) which was induced by N deficiency, can significantly affect the regulation of plant architecture response to N in rice. Under N deficiency, the mutation of OsSHR2 significantly reduced root growth, and impaired the sensitivity of the root meristem length to N deficiency. The mutants were found to have approximately a 15% reduction in plant height compared to wild type. But mutants showed a significant increase in tillering at post-heading stage, approximately 26% more than the wild type, particularly in high N conditions. In addition, due to reduced seed setting rate and 1000-grain weight, mutant yield was significantly decreased by approximately 33% under low N fertilizer supply. The mutation also changed the distribution of N between the vegetative and reproductive organs. Our findings suggest that the transcription factor OsSHR2 plays a regulatory role in the response of plant architecture and yield per plant to N in rice.

Essentiality for rice fertility and alternative splicing of OsSUT1.

Sucrose-proton symporters play important roles in carbohydrate transport during plant growth and development. Their physiological functions have only been partly characterized and their regulation mechanism is largely unclear. Here we report that the knockout of a sucrose transporter gene, OsSUT1, by CRISPR-Cas9 mediated gene editing resulted in a slightly dwarf size and complete infertility of the gene's homozygous mutants. Observation of caryopsis development revealed that the endosperm of OsSUT1 mutants failed to cellularize and did not show any sign of seed-filling. Consistently, OsSUT1 was identified to express strongly in developing caryopsis of wild-type rice, particularly in the nucellar epidermis and aleurone which are critical for the uptake of nutrients into the endosperm. These results indicate that OsSUT1 is indispensable during the rice reproductive stage particularly for caryopsis development. Interestingly, OsSUT1 possesses at least 6 alternative splicing transcripts, including the 4 transcripts deposited previously and the other two identified by us. The differences among these transcripts primarily lie in their coding region of the 3' end and 3' UTR region. Real-time PCR showed that 4 of the 6 transcripts had different expressional patterns during rice vegetative and reproductive growth stages. Given the versatility of the gene, addressing its alternative splicing mechanism may expand our understanding of SUT's function substantially.