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

TONETTI, TOMÁS; BRUNO E ROJAS; FIGUEROA, CARLOS M.

Mendoza

Congreso; SAIB; 2022

SAIB

Trehalose 6-phosphate (Tre6P) is a signal metabolite that coordinates plant carbon metabolism with growth and development. The Tre6P-sucrose nexus model postulates that Tre6P is a signal and a negative feedback regulator of sucrose levels. Our current understanding of Tre6P metabolism and signalling in plants is based almost entirely on studies performed with Arabidopsis thaliana, an eudicot performing C3 photosynthesis. To better understand the role of Tre6P in C4 species, we used Setaria viridis as a model species. In this work, we analysed the expression pattern of the genes involved in Tre6P metabolism, their intercellular distribution in leaves and the role of Tre6P in the regulation of sucrose export. Setaria has 21 putative genes coding for Tre6P-related enzymes: 10 Tre6P synthases (TPS), 10 Tre6P phosphatases (TPP) and 1 trehalase (TRE). To analyze their expression pattern, we performed real-time qPCR in the aerial part of five-days old seedlings, whole leaves (pool from leaves 5 and 6), the fourth internode, the flag leaf and inflorescences. The SvTPSI.1 transcript (encoding the SvTPSI.1 protein, putatively involved in Tre6P synthesis) was mainly found in whole leaves and the fourth internode. SvTPSII transcripts (encoding Class II TPS proteins, putatively involved in Tre6P perception and/or signaling) were preferentially accumulated in whole leaves and seedlings. SvTPP transcripts were detected in all the analyzed tissues, with higher levels in samples from whole leaves and the fourth internode. Analysis of samples enriched in mesophyll cells (MC) and bundle sheath cells (BSC) showed that the SvTPSI.1, SvTPPB1.1 and SvTPPB1.2 transcripts were mainly found in BSC. Finally, we incubated isolated BSC strands with different metabolites, including Tre6P, Glc6P, Suc and trehalose, to test their effect on the levels of transcripts preferentially accumulated in BSC. We found that incubation of BSC with Tre6P and Suc increased the levels of SvSWEET13a and SvSWEET13b. Our results strongly suggest that Tre6P metabolism occurs in BSC, where it would regulate sucrose export to the apoplast by modulating the expression and/or stability of transcripts encoding SWEET13 transporters.