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. 2021 Oct 8:12:728166.
doi: 10.3389/fgene.2021.728166. eCollection 2021.

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

Shiduo Niu  1 , Xiong Du  1 , Dejie Wei  1 , Shanshan Liu  1 , Qian Tang  1 , Dahong Bian  1 , Yarong Zhang  1 , Yanhong Cui  1 , Zhen Gao  1
Affiliations

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

Shiduo Niu et al. Front Genet. .

Abstract

Global warming has increased the occurrence of high temperature stress in plants, including maize, resulting in decreased the grain number and yield. Previous studies indicate that heat stress mainly damages the pollen grains and thus lowered maize grain number. Other field studies have shown that heat stress after pollination results in kernel abortion. However, the mechanism by which high temperature affect grain abortion following pollination remains unclear. Hence, this study investigated the field grown heat-resistant maize variety "Zhengdan 958" (ZD958) and heat-sensitive variety "Xianyu 335" (XY335) under a seven-day heat stress treatment (HT) after pollination. Under HT, the grain numbers of XY335 and ZD958 were reduced by 10.9% (p = 0.006) and 5.3% (p = 0.129), respectively. The RNA sequencing analysis showed a higher number of differentially expressed genes (DEGs) between HT and the control in XY335 compared to ZD958. Ribulose diphosphate carboxylase (RuBPCase) genes were downregulated by heat stress, and RuBPCase activity was significantly lowered by 14.1% (p = 0.020) in XY335 and 5.3% (p = 0.436) in ZD958 in comparison to CK. The soluble sugar and starch contents in the grains of XY335 were obviously reduced by 26.1 and 58.5%, respectively, with no distinct change observed in ZD958. Heat stress also inhibited the synthesis of grain starch, as shown by the low activities of metabolism-related enzymes. Under HT, the expression of trehalose metabolism genes in XY335 were upregulated, and these genes may be involved in kernel abortion at high temperature. In conclusion, this study revealed that post-pollination heat stress in maize mainly resulted in reduced carbohydrate availability for grain development, though the heat-resistant ZD958 was nevertheless able to maintain growth.

Keywords: assimilates; heat stress; kernel abortion; maize; trehalose.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Effects of heat stress on the kernel number of maize varieties (ZD958 and XY335) grown under control (CK) and heat treatment (HT) conditions.
FIGURE 2
FIGURE 2
(A) Effects of heat stress on ear growth rate after 5 days of heat treatment. CK and HT indicate the control and heat treatment, respectively. (B) Relationship between the ear growth rate after 5 days of heat treatment and the kernel number per plant.
FIGURE 3
FIGURE 3
Comparing the differentially expressed genes (DEGs) of maize varieties XY335 and ZD958 grown under both control (CK) and heat (HT) treatments on the 5th day of HT. (A) Total numbers of upregulated and downregulated genes (B) Venn diagram of the DGEs and (C) heatmap of the genes related to heat shock under heat stress.
FIGURE 4
FIGURE 4
Changes in photosynthesis after 5 days of heat treatment (HT) compared to the control (CK): (A) photosynthesis rate in CK and HT; (B) ribulose diphosphatecarboxylase (RuBPCase) activity in CK and HT; and (C) heatmap of the genes related to RuBPCase under heat stress. Red and blue lines represent upregulated and downregulated genes, respectively.
FIGURE 5
FIGURE 5
Effects of heat stress on soluble sugar, and starch content in the kernel and relationships between soluble sugar/starch with kernel number and ear growth rate. (A) Soluble sugar and starch contents in the maize kernels as affected by heat treatment (HT) after the 5th day of treatment. (B) The relationship between the soluble sugar (left)/starch (right) contents with final kernel number. (C) The relationships between the soluble sugar (left)/starch (right) contents with the ear growth rate.
FIGURE 6
FIGURE 6
Changes in the activities of starch synthase (SSS), adenosine diphosphate-glucose pyrophosphorylase (AGPase), and cell wall invertase (CWIN) at 5 days after heat treatment.
FIGURE 7
FIGURE 7
Expression profiles of genes that encode starch synthase (SSS), adenosine diphosphate-glucose pyrophosphorylase (ADGPase), and cell wall invertase (CWIN). (A) Gene expression (FPKM fold change) of the candidate genes in maize leaves under CK and HT conditions.
FIGURE 8
FIGURE 8
Variation in expression profiles of the genes involved in trehalose biosynthesis.
FIGURE 9
FIGURE 9
A schematic diagram model for the mechanism of kernel abortion, including transcripts, starch and sucrose metabolism and photosynthesis.
See this image and copyright information in PMC

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