A doubling of rice production per hectare is needed to meet the main calorific intake for half of the world's population by 2050 (Zhang 2007, Voesenek and Bailey-Serres 2009, Xing and Zhang 2010). Grain yield in rice is determined by three factors: number of panicles, number of grains per panicle, and grain weight (Xing and Zhang 2010, Zhang, Zhang et al. 2018). Grain weight is mainly determined by grain shape and size, which are in turn determined by grain length, width, thickness, and filling degree (Zhang, Wang et al. 2012). Once the number of grains per panicle and panicles per plant reach optimal levels, improvement in grain weight becomes important for further increasing grain yield in breeding programs (Jiao, Wang et al. 2010, Miura, Ikeda et al. 2010). Of these traits, grain weight is the most important, as it is measured as a 1,000-grain weight and is mainly restricted by grain shape, characterized by grain length, width, thickness, and filling degree (Xing and Zhang 2010, Huang, Jiang et al. 2013). These four parameters are positively correlated with grain weight. Several genes affecting grain size have been cloned from rice varieties through quantitative trait locus (QTL) analysis, to date GS3 (Fan, Xing et al. 2006, Takano-Kai, Jiang et al. 2009), qGL3/qGL3.1 (Zhang, Wang et al. 2012), GW2 (Song, Huang et al. 2007),GIF1 (He, Wang et al. 2012),GS5 (Li, Fan et al. 2011), and GL7/GW7 (Wang, Li et al. 2015, Wang, Xiong et al. 2015) have been isolated as genes that increase grain length. Among them, GS3 and qGL3/qGL3.1 are the main QTLs that regulate grain length by controlling the number of cells in glumes (Fan, Xing et al. 2006, Mao, Sun et al. 2010, Zhang, Wang et al. 2012). GW2, which encodes a RING-type E3 ubiquitin ligase, negatively regulates grain width, weight, and yield by negatively regulating cell division in the shell (Song, Huang et al. 2007, Ding, Lin et al. 2015). GS5 encodes a hypothetical serine carboxypeptidase that positively regulates grain size by regulating grain width, filling, and weight (He, Wang et al. 2012). GIF1 can positively control grain filling to improve crop yield or quality, or improve resistance or storage stability (He, Wang et al. 2012). OsSPL4 is a key regulator of grain size and provides a strategy for panicle architecture and grain size modification for yield improvement in rice.(Hu, Huang et al. 2021)
Rice (Oryza sativa) is one of the most important food sources, but crop yield is controlled by multiple genes simultaneously and is heavily influenced by the environment (Wing, Purugganan et al. 2018, Panda, Mishra et al. 2021, Liu, Minjuan et al. 2022). Abiotic stresses such as drought, high/low temperatures, and salinity cause substantial yield losses annually (Mittler 2006, Wang, Lu et al. 2016). Drought is a major environmental factor that adversely affects plant growth and limits agricultural productivity (Cui, Wang et al. 2016), therefore, understanding the mechanistic effects of drought stress on rice will contribute to better utilization of water resources in rice production(Yang, Yu et al. 2022). Genes and their molecular functions determining seed structure, components, and quality of rice(Li, Chen et al. 2022), the transcription factor AtNF-YB1 enables drought resistance in Arabidopsis thaliana.(Cui, Wang et al. 2016). Studies showed that OsGRP3 enhanced the drought resistance of rice(Xu, Dou et al. 2022), and AtEDT1/HDG11 gene enhanced the drought resistance and improved the yield of rice(Yu, Chen et al. 2013).
In eukaryotes, there are highly conserved unknown functional domain proteins (DUFs) that are part of several gene families encoding proteins whose functions are not yet characterized (Cui, Wang et al. 2016). Despite extensive research, there are still about 4,000 poorly understood DUFs, accounting for more than 22% of all entries in the Pfam database (El-Gebali, Mistry et al. 2019). Studies have shown that proteins containing DUF domains play important roles in plant growth and development, defense against diseases, and adaptive responses to stress. For example, ESK1, a member of the DUF231 domain protein in Arabidopsis, is a new negative regulator of cold stress (Xin, Mandaokar et al. 2007), while TBR and TBL3, two other members, are involved in cellulose synthesis and secondary cell wall deposition (Bischoff, Nita et al. 2010). Genes G1, TH1/BSG1, and AFD1 containing DUF640 affect plant height, flower development, and yield by regulating cell division and expansion-related genes (Yoshida, Suzaki et al. 2009, Li, Sun et al. 2012, Ren, Rao et al. 2016). A novel gene encoding a conserved DUF581 domain has been shown to enhance salt stress tolerance in Arabidopsis thaliana (Hou, Liang et al. 2013, Liu, Minjuan et al. 2022).
In this study, we cloned and identified the maize gene ZmDUF1645, which encodes the protein DUF1645 with an unknown function. One member of the DUF1645 protein family in Arabidopsis, AT1G23710, has been shown to be induced by various environmental stress factors, including salt, cold, drought, ABA, and oxidative stress. Several studies have also demonstrated that AT1G23710 expression is altered during processes such as cold acclimation, pollen germination, and pollen tube growth (Fowler and Thomashow 2002, Wang, Zhang et al. 2008, Cui, Wang et al. 2016). Upon overexpression of ZmDUF1645 in rice, we observed significant changes in agronomic traits such as grain length, width, weight, and ear length. Additionally, the expression of genes regulating grain type, such as GS3 and GW2, and some signal genes involved in cell cycle and division, such as CKDA1 and LOCs, were significantly altered in the overexpression lines of ZmDUF1645. However, this overexpression also reduced the tolerance of rice to drought stress.