Endogenous Hormones Inhibit Differentiation of Young Ears in Maize (Zea mays L.) Under Heat Stress

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 heatsensitive 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 acid 3 (GA 3), gibberellin acid 4 (GA 4), 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.

Heat Stress After Pollination Reduces Kernel Number in Maize by Insufficient Assimilates

“…This study used the heat-sensitive "Xianyu 335" (XY335)and heat-insensitive maize varietiy: "Zhengdan 958" (ZD958) (Wang et al, 2020a). Both are common maize varieties in China.…”

“…The rising levels of carbon dioxide in the atmosphere causes a greenhouse effect that results in increased temperatures and climatic changes (Xuan et al, 2020). Rising temperature is a global issue because of its impact on crop growth and yield (Wang et al, 2020a). Maize is more sensitive to heat stress (one of the most important abiotic stresses) than wheat and rice (Zhao et al, 2017;Zhang et al, 2019).…”

Genetics of Germination and Seedling Traits under Drought Stress in a MAGIC Population of Maize

“…Many candidate genes were associated with coleoptile length/root length ratio under well-watered conditions. In Li et al [ 69 ], the gene Zm00001d034129 ( Peroxidase 73 ) was associated with maize seedling leaves under cold and heat stress. The authors reported that common genes for both treatments were enriched in the hydrogen peroxidase metabolic process, which is the case of this gene.…”

“…This gene belongs to the ERF family, genes of which are important regulators involved in cold and heat stresses. This gene was up-regulated under cold and heat conditions in Li et al [ 69 ].…”

“…Genes involved in both heat and cold stresses were found to be associated with the CDW/RDW ratio. Zm00001d007181 encoding CML (CaM-like proteins), was up-regulated under both cold and heat stress [ 70 ] and Zm00001d007267 , which was mainly involved in photosynthesis, is a candidate gene identified as a possible hub gene involved in temperature stresses [ 69 ].…”