Functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system

Sucrose (SUC) is a signaling molecule with multiple physiological functions. G protein is a kind of receptor that converts extracellular first messenger into intracellular second messenger. However, it is little known that SUC interplays with G protein signaling in maize thermotolerance. In this work, using maize seedlings as materials, the interplay between SUC and G protein signaling in maize thermotolerance was investigated. The results indicate that heat stress-decreased survival percentage and tissue viability of the seedlings was mitigated by SUC. Similarly, heat stress-increased malondialdehyde content and electrolyte leakage also was reduced by SUC. These findings show that SUC can potentially enhance thermotolerance in maize seedlings. Also, SUC-enhanced thermotolerance was abolished by suramin (G protein inhibitor) and N-ethylmaleimide (SUC transport inhibitor), but enhanced by 3-O-methyl-D-glucose (G protein activator), indicating the interplay of SUC and G protein signaling in maize thermotolerance. To investigate the possible mechanism behind SUC-G protein interaction in enhancing maize thermotolerance, osmoregulation in mesocotyls of seedlings were evaluated before and after heat stress. The results suggest that osmolytes (SUC, glucose, fructose, total soluble sugar, proline, and glycine betaine) contents in mesocotyls under non-heat and heat stress were increased by SUC in varying degrees. Likewise, the osmolyte-metabolizing enzymes (sucrose-phosphate synthase, sucrose synthase, pyrroline-5-carboxylate synthase, ornithine aminotransferase, betaine-aldehyde dehydrogenase, and trehalase) activities were enhanced by SUC. Analogously, ZmSPS1, ZmSUS6, ZmP5CS, ZmOAT, ZmBADH, and ZmTRE1 expression in mesocotyls was up-regulated by SUC to different extent. These findings illustrate that the functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system.