In Silico Functional Analyses of SWEETs Reveal Cues for Their Role in AMF Symbiosis

Abstract

SWEETs are novel class of sugar effl uxers, which have unique functional role in plant biology. Besides nectar production, freezing tolerance, and transport of hexoses across tonoplast and growth-supporting role of pathogens, these SWEETs could have potential role in establishing powerful symbiotic relationship at the root interface and also in feeding to arbuscular mycorrhizal fungi (AMF) symbionts. The microarray or transcriptome expression of SWEET genes from colonized roots revealed that out of 28 Medicago SWEETs, three genes ( MtSWEET1b , MtSWEET3c , and MtSWEET12 ) were induced specifi cally due to AMF symbiosis. The root type specifi c expression of these three genes was also enhanced by AMF colonization in rice. The degree of expression of OsSWEET1b , OsSWEET3b , and OsSWEET12 was increased in colonized large lateral roots (LLRM) and crown roots (CRM), while OsSWEET3b and OsSWEET12 were induced in fi ne lateral roots (FLRM) and CRM, respectively. Promoter regions of these SWEETs represent critical motif elements (MYCS, PB1S, and PHR1) which play critical role in establishment of AMF symbiosis and phosphate starvation-induced responses, respectively. Taken together, these SWEETs have potential to be explored via functional genomics tools to understand feeding mechanisms to symbionts.

New insights into the evolution and functional divergence of the SWEET family in Saccharum based on comparative genomics

“…However, four of the eight orthologs, SWEET4c , SWEET6 , SWEET11b and SWEET14 , were expressed in the panicle tissues in sorghum [ 78 ], indicating that these 4 genes take part in sugar transport for reproductive rather than vegetative growth. Two of the rice orthologs, SWEET3b and SWEET12 were induced by arbuscular mycorrhizal fungi (AMF) symbiosis in the root tissues [ 83 ], indicating that SWEET3b and SWEET12 could have potential functions in creating symbiotic relationships at the root interface.…”

Physiological and transcriptomic response ofMedicago truncatulato colonization with high and low benefit arbuscular mycorrhizal fungi

“…We found that SWEET3.3 and SWEET12 were more strongly upregulated in Ri09-colonized roots ( Fig. 7F ); both are upregulated in arbusculated cortical cells in M. truncatula (Sameeullah et al 2016). Interestingly, SWEET7 and SWEET13 were more strongly induced in Ga165-colonized roots, but SWEETs perform diverse physiological functions, and their upregulation does not necessarily increase sugar transport to the fungus.…”

Correlative evidence for co-regulation of phosphorus and carbon exchanges with symbiotic fungus in the arbuscular mycorrhizalMedicago truncatula

“…SWEET proteins are pH-independent, bidirectional ST with broad representation in bacteria, plants, fungi and animals (Chen et al, 2010; Chen et al, 2012; Lin et al, 2014) with crucial roles in multiple biological processes. SWEET1b shows upregulation in M+ plants, similar to the rice gene OsSWEET1b (Samueelah et al, 2016) or potato genes StSWEET1a and StSWEET1b (Manck-Götzenberger & Requena, 2016). Closest characterized homologue is AtSWEET1 of thale cress ( Arabidopsis thaliana ), whose substrate specificity is higher for Glc and somewhat lower for Gal, but does not transfer Suc (Chen et al, 2010), so similar substrate specificity could be expected for SWEET1b as well.…”