Heat-induced modulation of growth parameters and gene expression profiles in maize (Zea mays L.) seedlings.

Background: Heat stress is a major constraint on global agriculture, significantly reducing crop productivity. Maize (Zea mays L.), an important cereal crop for food, feed, and bioenergy is highly sensitive to high temperatures stress, particularly during early growth stages which impair shoot and root development and ultimately reduced farm yield. At the molecular level, heat stress induces gene expression changes critical for thermotolerance, including the upregulation of heat shock proteins like hsp70 and activation of oxidative stress responses. The present study investigated the expression of heat shock protein 70 (hsp70), dehydrin2 (dhn2), stay-green gene (sgr2), and senescence-associated gene (sag) in maize seedlings subjected to heat stress over a time treatment of 1, 3, 6, 24, 48, and 72 h, respectively.

Methods And Results: Maize seeds were germinated and subjected to high temperture (36/41 °C). stress. The samples were collected multiple time points for growth and gene expression analysis. Heat stress significantly inhibited plant growth, reducing shoot fresh weight (SFW), dry weight (SDW), and the SFW/SDW ratio whereas, traits likes increasing root length (RL), root fresh weight (RFW), and the RFW/RDW ratio were elevated, respectively. For gene expression analysis, sequences for genes sag, sgr2, hsp70, and dhn2 were reterived from NCBI and analyzed using MEME, GSDS, and STRING databases. RNA was extracted from seedling shoots which was quantified and used to synthesize cDNA for quantitative RT-PCR, with EF1α as an internal control. Expression analysis displayed a transient upregulation (1.688-fold) of sag, sgr2, and hsp70 after 1 h of heat stress, while Dhn2 expression remained unchanged. The positive correlations between sag-dhn2, and hsp70-sgr2 and reduced hsp70 and sgr2 co-expression over time, suggest link to heat-induced senescence and dehydration.

Conclusion: Heat stress significantly affected maize seedling growth by reducing shoot biomass and enhancing root growth. Gene expression analysis revealed an initial upregulation of stress-related genes except dhn2 which shown downregulation. These findings suggest that heat-induced senescence and dehydration are linked, with reduced co-expression of hsp70 and sgr2 indicating a response to thermal stress.