The biosynthetic route for the synthesis of trehalose in plants is through a low-flux pathway that leads to the accumulation of micromolar amounts of trehalose 6-phosphate (T6P) and trehalose when sucrose is available. T6P accumulates in proportion to sucrose (Lunn et al., 2006) as an indispensable regulator of carbohydrate utilization (Schluepmann et al., 2003). At least some of the indispensability of T6P and its profound and widespread effects on plant growth and development can be explained through T6P inhibition of the SNF1-related protein kinase SnRK1 (Zhang et al., 2009), a central regulator of plant responses to carbon and energy status. Through T6P/SnRK1-mediated signaling, plant growth and development are regulated in line with sucrose availability by large-scale reprogramming of gene expression, which includes derepression of anabolic growth processes when carbon is available (Zhang et al., 2009). In crops, there are several emerging cases where T6P/SnRK1 can be modified to alter carbon use and allocation to improve yield under field conditions (Paul et al., 2020). The most successful route through which T6P has been genetically modified for yield and resilience so far is to alter trehalose phosphate phosphatase (TPP) activity. Ectopic expression of a TPP enzyme in maize reproductive tissue using the MADS-box transcription factor 6 (MADS6) gene promoter increased grain numbers in the field, especially under drought (Nuccio et al., 2015). Altered distribution of sucrose away from pith toward developing grain was associated with altered expression of genes encoding Sucrose Will Eventually Be Exported Transporters (SWEETs) and prevented abortion of grain under drought (Oszvald et al., 2018). In sorghum, it was found through genetic crosses of sweet and grain sorghum that a Basic Leucine Zipper Domain (bZIP) transcription factor elevated TPP expression, which underpinned the large differences in height of stems and accumulation of carbohydrates within stems of sweet and grain sorghum (Paul et al., 2020). A TPP gene in rice was found to underlie a quantitative trait locus for germination under flooded conditions through better mobilization of starch reserves, likely through SnRK1, providing promise for the development of direct-seeded rice (Paul et al., 2020).
