The Dual Function of OsSWEET3a as a Gibberellin and Glucose Transporter Is Important for Young Shoot Development in Rice

Abstract

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.

OsSWEET11b, a sixth leaf blight susceptibility gene involved in sugar transport-dependent male fertility

“…S17). This result is similar as described in a parallel study for LOC_Os09g32992 (defined here as OsSWEET11b), a gene not characterized further by the authors (Morii et al, 2020). Notably, substantial GA transport was also not detected for OsSWEET11a (Morii et al, 2020.…”

“…At present, it cannot be excluded that the observed GA transport activity is physiologically not relevant, and GA supplementation of sterility in Arabidopsis is due to indirect effects. Surprisingly, the evolution of GA transport capacity by SWEETs appears to emerge or gets lost during evolution independently (Morii et al, 2020). Dissection of the two activities by combination of structural and mutagenesis studies and further characterization of SWEETs may help to resolve this conundrum.…”

“…The SWEETs were highlighted based on the sucrose/GA transport capability. Blue color indicates the SWEETs capable of both sucrose/hexoses and GA transport while green and purple colors show the SWEETs only capable of sucrose/hexoses transport or GA transport activity has not been determined (Kanno et al, 2016;Morii et al, 2020). GA, gibberellic acid; n.d., not determined.…”

“…Surprisingly, a yeast three-hybrid (Y3H) screen had identified clade III SWEETs including AtSWEET13 and 14 as GA transporters, raising the possibility that the male sterility in double mutants was caused by either a defect in GA transport, or an indirect effect of a defect in sucrose transport on GA levels (Kanno et al, 2016). More recently, the clade I SWEET3a glucose transporter has been shown to be involved in GA transport (Morii et al, 2020). In rice, RNA interference of SWEET11 (Os8N3) also caused male sterility in rice (Yang et al, 2006).…”

Systematic Genome-Wide Study and Expression Analysis of SWEET Gene Family: Sugar Transporter Family Contributes to Biotic and Abiotic Stimuli in Watermelon

“…Sugar transporters are also involved in plant responses to phytohormones and abiotic stresses. The OsSWEET3a protein has a dual function in rice as a gibberellin (GA) and glucose transporter [42]. Both knockout and overexpression lines of OsSWEET3a showed defects in germination and early shoot development, and this phenotype can be restored by exogenous gibberellin application.…”