Abstract
As one of the abiotic stresses, low temperature severely threatens rice production during its entire growth period, especially during the booting stage. In the present study, transcriptome analysis was performed comparing Longjing (LJ) 25 (chilling-tolerant) and LJ 11 (chilling-sensitive) rice varieties to identify genes associated with chilling tolerance in rice spikelets. A total of 23 845 expressed genes and 13 205 differentially expressed genes (DEGs) were identified, respectively. Gene ontology (GO) enrichment analyses revealed ‘response to cold’ (containing 180 DEGs) as the only category enriched in both varieties during the entire cold treatment period. Through MapMan analysis, we identified nine and six DEGs related to the Calvin cycle and antioxidant enzymes, respectively, including OsRBCS3, OsRBCS2, OsRBCS4, OsAPX2 and OsCATC, that under chilling stress were markedly downregulated in LJ11 compared with LJ25. Furthermore, we predicted their protein–protein interaction (PPI) network and identified nine hub genes (the threshold of co-expressed gene number ≥ 11) in Cytoscape, including three RuBisCO-related genes with 14 co-expressed genes. Under chilling stress, antioxidant enzyme activities (peroxidase (POD) and catalase (CAT)) were downregulated in LJ11 compared with LJ25. However, the content of malondialdehyde (MDA) was higher in LJ11 compared with LJ25. Collectively, our findings identify low temperature responsive genes that can be effectively used as candidate genes for molecular breeding programmes to increase the chilling tolerance of rice.
Highlights
Growing plants are highly sensitive to and unable to escape from environmental stress
Previous research has shown that the development of tapetum cells from the tetrad to the young microspore stage (YM stage) was crucial to pollen maturation for it is the period most affected by low temperature
The purpose of our study was to identify low temperature responsive genes that can be effectively used to increase the chilling tolerance of rice grown in cold regions
Summary
Growing plants are highly sensitive to and unable to escape from environmental stress. Rice is threatened by low temperatures during its entire growing period, showing different responses to chilling stress during each growth stage, such as a low seed germination rate, chlorotic leaves, reduced culm length and reduced numbers of tillers during the germination stage and the vegetable stage. The booting stage is the most sensitive to low temperatures, and the chilling injury occurring during this stage is called obstructive chilling damage, which leads to pollen sterility and subsequent yield losses. CYP704B2 [4], OsUgp1 [5], OsUgp2 [6], OsMTR1 [7], Osg1 [8], OsC6 [9] and OSINV4 [10] are all functionally associated with tapetum development and, if disturbed by chilling stress, the resulting tapetum abnormity and pollen abortion will subsequently lead to a decline in yield. The tapetum is a model organ for plant PCD investigation, and several regulating genes associated with tapetum degradation have been reported, including TDR [11], DTC [12], OsMS1 [13], API5 [14], EAT1 [15], OsADF [11] and OsMYB80 [16]
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