Crosstalk of methylglyoxal and calcium signaling in maize (Zea mays L.) thermotolerance through methylglyoxal-scavenging system

Methylglyoxal (MG) and calcium ion (Ca²⁺) can increase multiple-stress tolerance including plant thermotolerance. However, whether crosstalk of MG and Ca²⁺ exists in the formation of maize thermotolerance and underlying mechanism still remain elusive. In this paper, maize seedlings were irrigated with MG and calcium chloride alone or in combination, and then exposed to heat stress (HS). The results manifested that, compared with the survival percentage (SP, 45.3%) of the control seedlings, the SP of MG and Ca²⁺ alone or in combination was increased to 72.4%, 74.2%, and 83.4% under HS conditions, indicating that Ca²⁺ and MG alone or in combination could upraise seedling thermotolerance. Also, the MG-upraised SP was separately weakened to 42.2%, 40.3%, 52.1%, and 39.4% by Ca²⁺ chelator (ethylene glycol tetraacetic acid, EGTA), plasma membrane Ca²⁺ channel blocker (lanthanum chloride, LaCl₃), intracellular Ca²⁺ channel blocker (neomycin, NEC), and calmodulin (CaM) antagonist (trifluoperazine, TFP). However, significant effect of MG scavengers N-acetylcysteine (NAC) and aminoguanidine (AG) on Ca²⁺-induced thermotolerance was not observed. Similarly, an endogenous Ca²⁺ level in seedlings was increased by exogenous MG under non-HS and HS conditions, while exogenous Ca²⁺ had no significant effect on endogenous MG. These data implied that Ca²⁺ signaling, at least partly, mediated MG-upraised thermotolerance in maize seedlings. Moreover, the activity and gene expression of glyoxalase system (glyoxalase I, glyoxalase II, and glyoxalase III) and non-glyoxalase system (MG reductase, aldehyde reductase, aldo-keto reductase, and lactate dehydrogenase) were up-regulated to a certain extent by Ca²⁺ and MG alone in seedlings under non-HS and HS conditions. The up-regulated MG-scavenging system by MG was enhanced by Ca²⁺, while impaired by EGTA, LaCl₃, NEC, or TFP. These data suggest that the crosstalk of MG and Ca²⁺ signaling in maize thermotolerance through MG-scavenging system. These findings provided a theoretical basis for breeding climate-resilient maize crop and developing smart agriculture.