AbstractBackground and AimsThe mechanisms of sugar sensing in grasses remain elusive, especially those using C4photosynthesis even though a large proportion of the world's agricultural crops utilize this pathway. We addressed this gap by comparing the expression of genes encoding components of sugar sensors in C3and C4grasses, with a focus on source tissues of C4grasses. Given C4plants evolved into a two-cell carbon fixation system, it was hypothesized this may have also changed how sugars were sensed.MethodsFor six C3and eight C4grasses, putative sugar sensor genes were identified for target of rapamycin (TOR), SNF1-related kinase 1 (SnRK1), hexokinase (HXK) and those involved in the metabolism of the sugar sensing metabolite trehalose-6-phosphate (T6P) using publicly available RNA deep sequencing data. For several of these grasses, expression was compared in three ways: source (leaf) versus sink (seed), along the gradient of the leaf, and bundle sheath versus mesophyll cells.Key ResultsNo positive selection of codons associated with the evolution of C4photosynthesis was identified in sugar sensor proteins here. Expressions of genes encoding sugar sensors were relatively ubiquitous between source and sink tissues as well as along the leaf gradient of both C4and C3grasses. Across C4grasses,SnRK1β1andTPS1were preferentially expressed in the mesophyll and bundle sheath cells, respectively. Species-specific differences of gene expression between the two cell types were also apparent.ConclusionsThis comprehensive transcriptomic study provides an initial foundation for elucidating sugar-sensing genes within major C4and C3crops. This study provides some evidence that C4and C3grasses do not differ in how sugars are sensed. While sugar sensor gene expression has a degree of stability along the leaf, there are some contrasts between the mesophyll and bundle sheath cells.