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We show that the knockout of a sugar transporter gene OsSWEET15 led to a significant drop in rice fertility with around half of the knockout mutant’s spikelets bearing blighted or empty grains. The rest of the spikelets bore fertile grains with a slightly reduced weight. Notably, the ovaries in the blighted grains of the ossweet15 mutants expanded after flowering but terminated their development before the endosperm cellularization stage and subsequently aborted. β- glucuronidase (GUS) and Green Fluorescent Protein (GFP) reporter lines representing the OsSWEET15 expression showed that the gene was expressed in the endosperm tissues surrounding the embryo, which supposedly supplies nutrients to sustain embryo development. These results together with the protein’s demonstrated sucrose transport capacity and plasma membrane localization suggest that OsSWEET15 plays a prominent role during the caryopsis formation stage, probably by releasing sucrose from the endosperm to support embryo development. By contrast, the empty grains were probably caused by the reduced pollen viability of the ossweet15 mutants. Investigation of ossweet11 mutant grains revealed similar phenotypes to those observed in the ossweet15 mutants. These results indicate that both OsSWEET15 and OsSWEET11 play important and similar roles in rice pollen development, caryopsis formation and seed-setting, in addition to their function in seed-filling that was demonstrated previously.

we show that the knockout of a sugar transporter gene OsSWEET15 led to a significant drop in rice fertility because near half of the knockout mutant spikelets bore blighted or empty grains. The rest spikelets bore fertile grains with slightly reduced weight. Notably, the ovaries in the blighted grains of the ossweet15 mutants expanded after flowering but terminated development before the endosperm cellularization stage and aborted subsequently. GUS and GFP representing OsSWEET15 expression showed that the protein was strongly expressed in the embryo surrounding region (ESR) which was supposed to supply nutrients for the embryo development. These results joined with the protein’s sucrose transport capacity and plasma membrane localization suggest that OsSWEET15 plays a prominent role during the caryopsis formation stage probably by releasing sucrose from the ESR to support the embryo development. By contrast, the empty grains were probably caused by the reduced pollen viability of the ossweet15 mutants. Investigation of the makeup of ossweet11 mutant grains revealed similar phenotypes that were observed in the ossweet15 mutants. These results indicate that both OsSWETT15 and OsSWEET11 play important and similar roles during rice pollen development, caryopsis formation, and seed-setting in addition to their function in seed-filling that was demonstrated previously.

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.

When spouting binary mixtures of fine and coarse particles, poor mixing and particle segregation are often observed under certain operating conditions. The underlying mechanism of particle segregation is considered to be related to inter-particle and intra-particle friction stresses. In this work, computational fluid dynamics (CFD) simulations with a multi fluid model (MFM) were employed to investigate the particle mixing and segregation in spouted beds with binary mixtures. Results show that when particle segregation occurs, coarse particles tend to circulate in the outer ring while fine particles are circulating in the inner circle. The mixing and segregation in the spouted bed of binary mixtures is greatly influenced by the particle density of coarse particles. This effect is more profound than that of the particle size of coarse particles used. The extent of particle segregation is found to decrease by increasing the spouting velocity. From the simulation results, particle segregation in a spouted bed of binary mixtures is observed in a region where there is a significant difference in the gas-solid drags of different particles.

The spouting of fine particles is significantly different from that of coarse particles and a stable spouting can only be obtained under very constrained operating conditions. However, the stability of a spouted bed with fine particles can be effectively improved by addition of coarse particles. In this work, the flow regime transition and hydrodynamics of spouted beds with binary mixtures were experimentally investigated under a broad range of operating parameters. Effects of particle size, density, mixing ratio, gas velocity and nozzle diameter on flow regime transition and minimum spouting velocity in spouted beds were explored. The results show that a moderate increase in the mean particle diameter and density due to addition of coarse particles is beneficial to spouting stability. However, segregation is also observed when adding excess amount of coarse particles, thus leading to decreased spouting stability.

When handling fine particles in spouted beds, addition of coarse particles has shown improved spouting stability than single particle systems. However, segregation may still occur because of insufficient mixing in binary mixtures, which will adversely influence the process performance. Therefore, in this study, analysis of pressure drop and its fluctuation signals were for the first time used to understand mechanisms of flow regime transitions in spouted beds with binary mixtures. The results showed that the typical varying sequence of pressure drop can be observed for spouted bed with binary mixtures and the peak pressure drop is related to the mixing degree of particles, which is mainly influenced by the inter-particle forces between fine particles and their counterpart coarse ones. The statistic characteristics of pressure drop time series, i.e., average value, standard deviation and probability distributions, were found to vary for different flow regimes. Therefore, they could be used for the characterization of these flow regimes. The spouting stability of binary mixtures can be reflected by power spectrum analysis; the influences of particles size and density difference on spouting stability were discussed through power spectral analysis.