Exogenous methylglyoxal alleviates drought-induced 'plant diabetes' and leaf senescence in maize.

Drought-induced leaf senescence is associated with high sugar levels, which bears some resemblance to the syndrome of diabetes in humans; however, the underlying mechanisms of such 'plant diabetes' on carbon imbalance and the corresponding detoxification strategy are not well understood. Here, we investigated the regulatory mechanism of exogenous methylglyoxal (MG) on 'plant diabetes' in maize plants under drought stress applied via foliar spraying during the grain-filling stage. Exogenous MG delayed leaf senescence and promoted photoassimilation, thereby reducing the yield loss induced by drought by 14%. Transcriptome and metabolite analyses revealed that drought increased sugar accumulation in leaves through inhibition of sugar transporters that facilitate phloem loading. This led to disequilibrium of glycolysis and overaccumulation of endogenous MG. Application of exogenous MG up-regulated glycolytic flux and the glyoxalase system that catabolyses endogenous MG and glycation end-products, ultimately alleviating 'plant diabetes'. In addition, the expression of genes facilitating anabolism and catabolism of trehalose-6-phosphate was promoted and suppressed by drought, respectively, and exogenous MG reversed this effect, implying that trehalose-6-phosphate signaling in the mediation of 'plant diabetes'. Furthermore, exogenous MG activated the phenylpropanoid biosynthetic pathway, promoting the production of lignin and phenolic compounds, which are associated with drought tolerance. Overall, our findings indicate that exogenous MG activates defense-related pathways to alleviate the toxicity derived from 'plant diabetes', thereby helping to maintain leaf function and yield production under drought.

Phosphorus deficiency promotes root:shoot ratio and carbon accumulation via modulating sucrose utilization in maize.

Phosphorus deficiency usually promotes root:shoot ratio and sugar accumulation. However, how the allocation and utilization of carbon assimilates are regulated by phosphorus deficiency remains unclear. To understand how phosphorus deficiency affects the allocation and utilization of carbon assimilates, we systematically investigated the fixation and utilization of carbon, along with its diurnal and spatial patterns, in hydroponically grown maize seedlings under low phosphorus treatment. Under low phosphorus, sucrolytic activity was slightly inhibited by 12.0% in the root but dramatically inhibited by 38.8% in the shoot, corresponding to the promoted hexose/sucrose ratio and biomass in the root. Results point to a stable utilization of sucrose in the root facilitating competition for more assimilates, while increasing root:shoot ratio. Moreover, starch and sucrose accumulated in the leaves under low phosphorus. Spatially, starch and sucrose were oppositely distributed, starch mainly in the leaf tip, and sucrose mainly in the leaf base and sheath. Evidence of sucrose getting stuck in leaf base and sheath suggests that carbon accumulation is not attributed to carbon assimilation or export disturbance, but may be due to poor carbon utilization in the sinks. These findings improve the understanding of how low phosphorus regulates carbon allocation between shoot and root for acclimation to stress, and highlight the importance of improving carbon utilization in sinks to deal with phosphorus deficiency.

Stubby or Slender? Ear Architecture Is Related to Drought Resistance in Maize.

Ear architecture is determined by two stable heritable traits, kernel row number (KRN) and kernel number per row (KNPR), but its relationship with drought resistance is still vague. To this end, we obtained 16 and 11 hybrids with slender (less KRN but more KNPR) and stubby (more KRN but less KNPR) ears by intentionally crossbreeding, respectively. These hybrids were exposed to a seven-day water deficit (WD) since silk emergence coupled with synchronous (SP) and continuous pollination (CP) to alter the pollination time gaps on ears. The results showed that the emerged silks in CP were 9.1 and 9.0% less than in the SP treatment in the stubby and slender ears, respectively, suggesting the suppression of asynchronous pollination on silk emergence. The stubby ears performed higher silking rate and yield compared with the slender ears with or without drought stress. To eliminate the inherent difference in sink capacities, we selected four hybrids for each ear type with similar silk and kernel numbers for further analyses. Interestingly, the stubby ears were less affected in silking rate and thus performed higher yield under drought compared with the slender ears. The finding suggests that ear architecture matters in the determination of drought resistance that deserves more attention in breeding.