Abstract
Seed setting rate is one of the major components that determine rice (Oryza sativa L.) yield. Successful fertilization is necessary for normal seed setting. However, little is known about the molecular mechanisms governing this process. In this study, we report a novel rice gene, LOW SEED SETTING RATE1 (LSSR1), which regulates the seed setting rate by facilitating rice fertilization. LSSR1 encodes a putative GH5 cellulase, which is highly conserved in plants. LSSR1 is predominantly expressed in anthers during the microsporogenesis stage, and its encoded protein contains a signal peptide at the N-terminal, which may be a secretory protein that stores in pollen grains and functions during rice fertilization. To explore the physiological function of LSSR1 in rice, loss-of-function mutants of LSSR1 were created through the CRISPR-Cas9 system, which showed a significant decrease in rice seed setting rate. However, the morphology of the vegetative and reproductive organs appears normal in lssr1 mutant lines. In addition, lssr1 pollen grains could be normally stained by I2-KI solution. Cytological results demonstrate that the blockage of fertilization mostly accounted for the low seed setting rate in lssr1 mutant lines, which was most likely caused by abnormal pollen grain germination, failed pollen tube penetration, and retarded pollen tube elongation. Together, our results suggest that LSSR1 plays an important role in rice fertilization, which in turn is vital for maintaining rice seed setting rate.
Highlights
Rice (Oryza sativa L.), the staple food of more than half of the world’s population distributed in Africa and Asia, is critical for global food security (Seck et al 2012)
LOW SEED SETTING RATE1 (LSSR1) is predominantly expressed in anthers during the stage of microsporogenesis A previous microarray analysis suggested that LOW SEED SETTING RATE 1 (LSSR1; LOC_Os02g38260) is predominantly expressed in meiotic and single-cell pollen stage anthers (Deveshwar et al 2011), while the data on the Rice eFP Browser shows that the expression of LSSR1 in meiotic panicles is not dominant (Additional file 1: Figure S1)
Traces of LSSR1 transcripts were detected in rice stems, sheaths, florets turning to green (FWTG), florets with mature reproductive organs (FM), and florets at 5–10 min after flowering (FAF) (Fig. 1a)
Summary
Rice (Oryza sativa L.), the staple food of more than half of the world’s population distributed in Africa and Asia, is critical for global food security (Seck et al 2012). Grain number per panicle, grain weight, and seed setting rate are the major components that determine rice yield. Recent results have shed some light on the molecular regulation of the seed setting rate in rice (Zhou et al 2011; Li et al.2013; Zhu et al 2017), much remains unknown. Climate variation may result in huge losses of rice yield, since the seed setting rate is susceptible to environmental conditions. Identifying more genes that control rice seed setting rate and detailing their genetic mechanisms, as well as their application in rice product is of critical importance for the maintenance and improvement of rice yield
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