Transgenic maize (Zea mays) that expresses rice (Oryza sativa) TREHALOSE PHOSPHATE PHOSPHATASE1 (TPP1) from the rice MADS6 promoter, which is active over the flowering period, produces higher yields than wild type. This yield increase occurs with or without drought conditions during flowering. To understand the mechanistic basis of the increased yield, we characterized gene expression and metabolite profiles in leaves and developing female reproductive tissue, comprising florets, node, pith, and shank, over the flowering period with and without drought. The MADS6 promoter was most active in the vasculature, particularly phloem companion cells in florets and pith, consistent with the largest decreases in trehalose 6-phosphate (T6P) levels (2- to 3-fold) being found in pith and florets. Low T6P led to decreased gene expression for primary metabolism and increased gene expression for secondary metabolism, particularly lipid-related pathways. Despite similar changes in gene expression, the pith and floret displayed opposing assimilate profiles: sugars, sugar phosphates, amino acids, and lipids increased in florets, but decreased in pith. Possibly explaining this assimilate distribution, seven SWEET genes were found to be up-regulated in the transgenic plants. SnRK1 activity and the expression of the gene for the SnRK1 beta subunit, expression of SnRK1 marker genes, and endogenous trehalose pathway genes were also altered. Furthermore, leaves of the transgenic maize maintained a higher photosynthetic rate for a longer period compared to wild type. In conclusion, we found that decreasing T6P in reproductive tissues down-regulates primary metabolism and up-regulates secondary metabolism, resulting in different metabolite profiles in component tissues. Our data implicate T6P/ SnRK1 as a major regulator of whole-plant resource allocation for crop yield improvement.

T6P can be targeted through genetic and chemical methods for crop yield improvements in different environments through the effect of T6P on carbon allocation and biosynthetic pathways.

Little is known about how salt impacts primary metabolic pathways of C₄ plants, particularly related to kernel development and seed set. Osmotic stress was applied to maize (Zea mays) B73 by irrigation with increasing concentrations of NaCl from the initiation of floral organs until 3 d after pollination. At silking, photosynthesis was reduced to only 2% of control plants. Salt treatment was found to reduce spikelet growth, silk growth, and kernel set. Osmotic stress resulted in higher concentrations of sucrose (Suc) and hexose sugars in leaf, cob, and kernels at silking, pollination, and 3 d after pollination. Citric acid cycle intermediates were lower in salt-treated tissues, indicating that these sugars were unavailable for use in respiration. The sugar-signaling metabolite trehalose-6-phosphate was elevated in leaf, cob, and kernels at silking as a consequence of salt treatment but decreased thereafter even as Suc levels continued to rise. Interestingly, the transcripts of trehalose pathway genes were most affected by salt treatment in leaf tissue. On the other hand, transcripts of the SUCROSE NONFERMENTING-RELATED KINASE1 (SnRK1) marker genes were most affected in reproductive tissue. Overall, both source and sink strength are reduced by salt, and the data indicate that trehalose-6-phosphate and SnRK1 may have different roles in source and sink tissues. Kernel abortion resulting from osmotic stress is not from a lack of carbohydrate reserves but from the inability to utilize these energy reserves.

Large differences exist in the number of grains per spikelet across an individual wheat (Triticum aestivum L.) spike. The central spikelets produce the highest number of grains, while apical and basal spikelets are less productive, and the most basal spikelets are commonly only developed in rudimentary form. Basal spikelets are delayed in initiation, yet they continue to develop and produce florets. The precise timing or the cause of their abortion remains largely unknown. Here, we investigated the underlying causes of basal spikelet abortion using shading applications in the field. We found that basal spikelet abortion is likely to be the consequence of complete floret abortion, as both occur concurrently and have the same response to shading treatments. We detected no differences in assimilate availability across the spike. Instead, we show that the reduced developmental age of basal florets pre-anthesis is strongly associated with their increased abortion. Using the developmental age pre-abortion, we were able to predict final grain set per spikelet across the spike, alongside the characteristic gradient in the number of grains from basal to central spikelets. Future efforts to improve spikelet homogeneity across the spike could thus focus on improving basal spikelet establishment and increasing floret development rates pre-abortion.

The majority of flowering-plant species can survive complete air-dryness in their seed and/or pollen. Relatively few species (‘resurrection plants’) express this desiccation tolerance in their foliage. Knowledge of the regulation of desiccation tolerance in resurrection plant foliage is reviewed. Elucidation of the regulatory mechanism in resurrection grasses may lead to identification of genes that can improve stress tolerance and yield of major crop species. Well-hydrated leaves of resurrection plants are desiccation-sensitive and the leaves become desiccation tolerant as they are drying. Such drought-induction of desiccation tolerance involves changes in gene-expression causing extensive changes in the complement of proteins and the transition to a highly-stable quiescent state lasting months to years. These changes in gene-expression are regulated by several interacting phytohormones, of which drought-induced abscisic acid (ABA) is particularly important in some species. Treatment with only ABA induces desiccation tolerance in vegetative tissue of Borya constricta Churchill. and Craterostigma plantagineum Hochstetter. but not in the resurrection grass Sporobolus stapfianus Gandoger. Suppression of drought-induced senescence is also important for survival of drying. Further research is needed on the triggering of the induction of desiccation tolerance, on the transition between phases of protein synthesis and on the role of the phytohormone, strigolactone and other potential xylem-messengers during drying and rehydration.

Trehalose 6‐phosphate (T6P) signalling regulates carbon use and allocation and is a target to improve crop yields. However, the specific contributions of trehalose phosphate synthase (TPS) and trehalose phosphate phosphatase (TPP) genes to source‐ and sink‐related traits remain largely unknown. We used enrichment capture sequencing on TPS and TPP genes to estimate and partition the genetic variation of yield‐related traits in a spring wheat (Triticum aestivum) breeding panel specifically built to capture the diversity across the 75,000 CIMMYT wheat cultivar collection. Twelve phenotypes were correlated to variation in TPS and TPP genes including plant height and biomass (source), spikelets per spike, spike growth and grain filling traits (sink) which showed indications of both positive and negative gene selection. Individual genes explained proportions of heritability for biomass and grain‐related traits. Three TPS1 homologues were particularly significant for trait variation. Epistatic interactions were found within and between the TPS and TPP gene families for both plant height and grain‐related traits. Gene‐based prediction improved predictive ability for grain weight when gene effects were combined with the whole‐genome markers. Our study has generated a wealth of information on natural variation of TPS and TPP genes related to yield potential which confirms the role for T6P in resource allocation and in affecting traits such as grain number and size confirming other studies which now opens up the possibility of harnessing natural genetic variation more widely to better understand the contribution of native genes to yield traits for incorporation into breeding programmes.