Abstract
Global warming frequently leads to extreme temperatures, which pose a serious threat to the growth, development, and yield formation of crops such as maize. This study aimed to deeply explore the molecular mechanisms of young ear development under heat stress. We selected the heat-tolerant maize variety Zhengdan 958 (T) and heat-sensitive maize variety Xianyu 335 (S), and subjected them to heat stress in the V9 (9th leaf), V12 (12th leaf), and VT (tasseling) growth stages. We combined analysis of the maize phenotype with omics technology and physiological indicators to compare the differences in young ear morphology, total number of florets, floret fertilization rate, grain abortion rate, number of grains, and main metabolic pathways between plants subjected to heat stress and those left to develop normally. The results showed that after heat stress, the length and diameter of young ears, total number of florets, floret fertilization rate, and number of grains all decreased significantly, whereas the length of the undeveloped part at the top of the ear and grain abortion rate increased significantly. In addition, the differentially expressed genes (DEGs) in young ears were significantly enriched in the hormone signaling pathways. The endogenous hormone content in young ears exhibited different changes: zeatin (ZT) and zeatin riboside (ZR) decreased significantly, but gibberellin acid3 (GA3), gibberellin acid4 (GA4), and abscisic acid (ABA) increased significantly, in ears subjected to heat stress. In the heat-tolerant maize variety, the salicylic acid (SA), and jasmonic acid (JA) content in the vegetative growth stage also increased in ears subjected to heat stress, whereas the opposite effect was observed for the heat-sensitive variety. The changes in endogenous hormone content of young ears that were subjected to heat stress significantly affected ear development, resulting in a reduction in the number of differentiated florets, fertilized florets and grains, which ultimately reduced the maize yield.
Highlights
In many parts of the world, temperatures hit record highs in 2019
The total number of florets in young ears decreased significantly after heat stress in 2 years. 2018 for example, despite having a different capacity for heat tolerance, both maize varieties showed that the most significant decrease happened during the V9 stage, for which the decrease reached 21.07% for the heat-tolerant variety and 12.06% for the heat-sensitive variety
When heat stress was applied during the V12 or VT stage, the total number of florets showed a greater decrease in the heat-sensitive maize variety (Figure 3A)
Summary
In many parts of the world, temperatures hit record highs in 2019. Ears Respond to Heat Stress temperatures have become a global problem affecting crop growth and yield. It has been predicted that the global temperature will increase by 1.5–6◦C in the future (Müller et al, 2017), causing the expectation that heat stress will become the main abiotic stress factor for crop production in times to come. Due to the increasing gap between the supply and demand for maize, maintaining the total maize yield is a priority. This requires clarification of the molecular mechanisms involved in responses of maize to heat stress, improving its thermotolerance, and increasing the yield per unit area
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