Trehalose 6-phosphate modulates the levels of SWEET13 transcripts in bundle sheath cells from Setaria viridis leaves

TONETTI T; ROJAS BE; FIGUEROA CM

Mendoza

Congreso; LVIII Reunión Anual de la SAIB; 2022

SAIB

Trehalose6-phosphate (Tre6P) is a signal metabolite that coordinates plant carbonmetabolism with growth and development. The Tre6P-sucrose nexus modelpostulates that Tre6P is a signal and a negative feedback regulator of sucroselevels. Our current understanding of Tre6P metabolism and signalling in plantsis based almost entirely on studies performed with Arabidopsis thaliana,an eudicot performing C3 photosynthesis. To better understand the role of Tre6Pin C4 species, we used Setaria viridis as a model species. In this work, weanalysed the expression pattern of the genes involved in Tre6P metabolism,their intercellular distribution in leaves and the role of Tre6P in theregulation of sucrose export. Setaria has 21 putative genes coding forTre6P-related enzymes: 10 Tre6P synthases (TPS), 10 Tre6P phosphatases (TPP)and 1 trehalase (TRE). To analyze their expression pattern, we performedreal-time qPCR in the aerial part of five-days old seedlings, whole leaves (poolfrom leaves 5 and 6), the fourth internode, the flag leaf and inflorescences.The SvTPSI.1 transcript (encoding the SvTPSI.1 protein, putatively involved inTre6P synthesis) was mainly found in whole leaves and the fourth internode.SvTPSII transcripts (encoding Class II TPS proteins, putatively involved inTre6P perception and/or signaling) were preferentially accumulated in wholeleaves and seedlings. SvTPP transcripts were detected in all the analyzedtissues, with higher levels in samples from whole leaves and the fourthinternode. Analysis of samples enriched in mesophyll cells (MC) and bundlesheath cells (BSC) showed that the SvTPSI.1, SvTPPB1.1 and SvTPPB1.2transcripts were mainly found in BSC. Finally, we incubated isolated BSCstrands with different metabolites, including Tre6P, Glc6P, Suc and trehalose,to test their effect on the levels of transcripts preferentially accumulated inBSC. We found that incubation of BSC with Tre6P and Suc increased the levels ofSvSWEET13a and SvSWEET13b. Our results strongly suggest that Tre6P metabolismoccurs in BSC, where it would regulate sucrose export to the apoplast bymodulating the expression and/or stability of transcripts encoding SWEET13transporters.