Molecular Plant Breeding 2024, Vol.15, No.6, 429-441 http://genbreedpublisher.com/index.php/mpb 434 reproductive development, including male fertility. For instance, drought stress during the reproductive stage can lead to aberrant anther development and reduced pollen viability, as observed in rice plants subjected to water stress (Jin et al., 2013). Additionally, water stress can disrupt carbohydrate metabolism and phytohormone signaling, further complicating the plant's physiological responses (Jin et al., 2013). 4.2 Water-responsive gene expression in rice The expression of genes in rice is highly responsive to water stress. Under drought conditions, a multitude of genes are differentially expressed to mediate stress responses. For example, a meta-analysis of microarray data identified numerous drought-responsive genes, including those involved in abiotic stimulus response, water deprivation, and abscisic acid (ABA) signaling (Soltanpour et al., 2022). These genes play crucial roles in modulating physiological processes to enhance drought tolerance. Similarly, specific TFs such as OsAL5 have been shown to regulate both drought-related genes and TGMS genes, linking drought response to MS (Wen et al., 2021). 4.3 Influence of drought and flooding on MS genes Drought and flooding have distinct yet profound effects on the expression of MS genes in rice. Drought stress can lead to the down-regulation of genes involved in pollen development, resulting in MS. For instance, genes associated with tapetum and microspore development are often down-regulated under drought conditions, leading to defective pollen development and reduced fertility (Jin et al., 2013). Conversely, flooding can also impact MS by altering the expression of stress-responsive genes. For example, low water temperatures before panicle initiation can increase chilling-induced MS and down-regulate stress-responsive genes such as OsFKBP65 and heat shock proteins, which are crucial for protecting proteins from oxidative damage (Suzuki et al., 2015). 4.4 Adaptive mechanisms in water-responsive MS Rice plants have evolved various adaptive mechanisms to cope with water stress and maintain MS. One such mechanism involves the regulation of reactive oxygen species (ROS) scavenging. The gene OsPP18, regulated by the TF SNAC1, enhances drought and oxidative stress tolerance by modulating ROS homeostasis through ABA-independent pathways (You et al., 2014). Additionally, the overexpression of OsAL5 has been shown to improve drought tolerance by regulating both drought-related genes and MS genes, suggesting a potential strategy for breeding drought-tolerant rice varieties with stable MS (Wen et al., 2021). These adaptive responses highlight the complex interplay between water stress and male sterility gene regulation in rice. 4.5 Impact of humidity on HGMS lines HGMS is a new type of EGMS discovered in rice recent year, which normally shows fertility under high humidity and sterility under low humidity. For instance, the spontaneous sterile mutant from the japonica rice cultivar ZH11, has defects in the structure of the pollen wall, and the pollen is prone to dehydration and inactivation in low humidity environments, but remains viable in high humidity environments (Xue et al., 2018; Chen et al., 2020). In the natural field conditions of Guangzhou, China (24°C~35°C, 50%~90% RH), this mutant showed a significantly reduced seed-setting rate (c. 10%) compared with that of ZH11 (Chen et al., 2020). Xue et al. (2018) demonstrate that deficiency of a triterpene pathway results in HGMS in rice, OsOSC12/OsPTS1 encodes a triterpene synthase, which affects the biosynthesis of C16 and C18 fatty acids in tryphine and regulates HGMS in rice. Another study reveals the molecular mechanism by which the rice HMS1 and HMS1I genes interact to regulate the synthesis of very-long-chain fatty acids and the formation of the oil layer in the pollen wall, thereby controlling HGMS (Figure 4) (Chen et al., 2020). 5 Cross-Talk Between Environmental Factors 5.1 Interaction between temperature and light in gene regulation The interaction between temperature and light plays a crucial role in the regulation of MS genes in rice. P/TGMS rice lines, such as Peiai64S (PA64S), exhibit fertility changes in response to varying temperature and light conditions. Studies have shown that the expression of microRNAs (miRNAs) and their target genes, which are involved in fatty acid metabolism and phenylalanine metabolism, are significantly influenced by temperature changes under long light conditions. Specifically, miR156, miR5488, and miR399 have been identified as key
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