Translocation and long-distance transport of phytohormones are considered important processes for phytohormone responses as well as their synthesis and signaling. Here, we report on the dual function of OsSWEET3a, a bidirectional sugar transporter from Clade I of the rice SWEET family of proteins, as both a gibberellin (GA) and a glucose transporter. OsSWEET3a efficiently transports GAs in the C13-hydroxylation pathway of GA biosynthesis. Both knockout and overexpression lines of OsSWEET3a showed defects in germination and early shoot development, which were partially restored by GA, especially GA20. Quantitative reverse transcription PCR, GUS staining, and in situ hybridization revealed that OsSWEET3a was expressed in vascular bundles in basal parts of the seedlings. OsSWEET3a expression co-localized with OsGA20ox1 expression in the vascular bundles but not with OsGA3ox2, whose expression was restricted to leaf primordia and young leaves. These results suggest that OsSWEET3a is expressed in the vascular tissue of basal parts of seedlings and is involved in the transport of both GA20 and glucose to young leaves, where GA20 is possibly converted to the bioactive GA1 form by OsGA3ox2, during early plant development. We also indicated that such GA transport activities of SWEET proteins have sporadically appeared in the evolution of plants: GA transporters in Arabidopsis evolved from sucrose transporters, while those in rice and sorghum have evolved from glucose transporters.

Proper anther and pollen development are important for plant reproduction. The plant hormone gibberellin is important for anther development in rice, but its gametophytic functions remain largely unknown. Here, we report the functional and evolutionary analyses of rice gibberellin 3-oxidase 1 (OsGA3ox1), a gibberellin synthetic enzyme specifically expressed in the late developmental stages of anthers. Enzymatic and X-ray crystallography analyses reveal that OsGA3ox1 has a higher GA7 synthesis ratio than OsGA3ox2. In addition, we generate an osga3ox1 knockout mutant by genome editing and demonstrate the bioactive gibberellic acid synthesis by the OsGA3ox1 action during starch accumulation in pollen via invertase regulation. Furthermore, we analyze the evolution of Oryza GA3ox1s and reveal that their enzyme activity and gene expression have evolved in a way that is characteristic of the Oryza genus and contribute to their male reproduction ability.

Microfluidic liquid cells have been developed to visualize nanoscaled biological samples in liquid using a scanning electron microscope (SEM) through an electron-transparent membrane (ETM). However, despite the combination of the high-resolution visualization of SEM and the high experimental capability of microfluidics, the image is unclear because of the scattering of the electron beam in the ETM. Thus, this study developed a microfluidic liquid cell with a super-thin ETM of thickness 10 nm. Because the super-thin ETM is excessively fragile, the bonding of a silicon–nitride-deposited substrate and a polydimethylsiloxane microchannel before silicon anisotropic etching was proposed prevented the super-thin ETM from damage and breakage due to etching. With this protection against etchant using the microchannel, the yield of the fabricated super-thin ETM increased from 0 to 87%. Further, the scattering of the electron beam was suppressed using a microfluidic liquid cell with a super-thin ETM, resulting in high-resolution visualization. In addition, T4 bacteriophages were visualized using a super-thin ETM in vacuum. Furthermore, the cyanobacterium Synechocystis sp. PCC6803 in liquid was visualized using a super-thin ETM, and sub-microscopic structures on the surface were observed.