In this study, two wheat varieties, Indian Blue Grain and Lango, were crossed. After several generations of self-crossing the F1 from Indian Blue Grain and Lango to select characters, the special wheat line DB-W was obtained. The leaves of DW-B display albinism after vernalization at low temperature and then return to green in the spring. In addition, DW-B is semi-dwarfing with blue grains. A comparative transcriptome analysis of DW-B and its parents at the early joining stage produced DEGs that were obtained and analyzed to study the mechanism of dwarfing and albinism.
Since the 1960s, researchers improved crop yields by reducing plant height in the first Green Revolution (Jiang, Li, et al., 2012, Peng, Richards, et al., 1999) (Hedden, 2003). Several of these height-related genes have been isolated and identified in studies to date, including RhtB1b, RhtD1b, Rth8, and Rht24, that were found to reduce plant height through the GA pathway (Si, Wang, et al., 2021, Tian, Xia, et al., 2022, Xiong, Zhou, et al., 2022). GA is an important factor in determining plant height by influencing the length and number of internode cells (Wang, Yin, et al., 2019). The signal transduction pathway of GA has been delineated (Yamaguchi, 2008). GID1 and DELLA are two key proteins in the GA signal transduction pathway. After binding GA, the GID1 protein interacts with two DELLA proteins to form the GA/GID1/DELLA complex (Ueguchi-Tanaka, Ashikari, et al., 2005, Ueguchi-Tanaka, Nakajima, et al., 2007). The DELLAs were then degraded by the 26S proteasome (Griffiths, Murase, et al., 2006). The degradation of DELLA proteins mitigated the induction of growth inhibition by DELLA and led to the induction of growth by GA. In this study, DW-B and Lango were not sensitive to GA, while Indian Blue Grain was sensitive to GA treatment, indicating that the dwarfing of DW-B originated from Lango and was related to GA signal transduction. A transcriptome analysis indicated that the GID1 gene was downregulated, and the DELLA protein-related genes were upregulated in DB-W. Thus, the defect in GA signaling pathway was the primary reason for the dwarfing of DB-W and Lango.
The biosynthesis and accumulation of pigments in plant leaves is regulated by genetics and the environment (Hu, Shi, et al., 2003). Leaf color mutants and the genes that regulate chloroplast and Chl biosynthesis have been reported in many plant species, including Arabidopsis, rice, maize, and tomato (Solanum tuberosum L.) (Barry, Aldridge, et al., 2012, Lin, Lee, et al., 2014, Shi, Zheng, et al., 2013, Zhou, Ren, et al., 2013). The dysfunctional chloroplast mutants usually had yellow or albino leaves. In addition, abnormal plastid number and development could lead to the impairment of thylakoid membrane formation and a reduction in the accumulation of Chl a/b-binding proteins in complexes I and II (Barry, Aldridge, et al., 2012). The degreening of leaves is caused by inhibition of the expression of genes involved in Chl biosynthesis or development (Chen, Bi, et al., 2005, Motohashi, Ito, et al., 2003). In our study, the concentration of Chl in DW-B was obviously different from that of Indian Blue Grain but similar to that of Lango, which also whitened. Owing to the restriction of Chl biosynthesis, the normal growth of DW-B can be satisfied by improving the photosynthetic characteristics of DW-B. In this study, the measurements of the contents of Chl and its fluorescence showed that there was a low concentration of Ct value in the DW-B leaves. This finding suggests that the DW-B leaves exhibit typical albinism in their cells and could be an ideal sample to study the mechanism of albinism. The protein-encoding hemC and hemD catalyze the conversion of PBG to UroIII and could play an important role in Chl biosynthesis. The enzymatic activity of UROS, which is encoded by hemD, decreased significantly in the DW-B leaves. This indicated that the decrease in Chl biosynthesis in albino leaves could be caused by the inhibition of hemD. However, a transcriptome analysis and qRT-PCR showed that the level of expression of hemD in the DW-B leaves was upregulated compared with that in the Indian Blue Grain leaves. This could indicate that the function of hemD protein is actually inhibited despite an increase in the level of expression of hemD in the DW-B leaves. This suggested that the function of UROS could be a key factor in the biosynthesis of Chl in albino leaf cells. There could be other factors, such as single nucleotide polymorphisms and methylation, that adversely affect the function of hemD proteins. Further studies are needed to analyze the translation and modification of hemD protein and the regulation of protein activity. Chloroplast development is often associated with many chloroplast genes, such as the GLK (Golden 2-like) gene family that includes GLK1 and GLK2 (Fitter, Martin, et al., 2002, Yasumura, Moylan, et al., 2005), the ARC (Accumulation and replication of chloroplast) gene family that includes ARC3, ARC5 and ARC6 (Gao, Kadirjan-Kalbach, et al., 2003, Shimada, Koizumi, et al., 2004, Vitha, Froehlich, et al., 2003), and the FKBP (FK506-binding proteins) gene (Gollan and Bhave, 2010). In this study, with the help of transcriptome analysis, relevant evidence could not be found, and a mor thorough analysis should be conducted in subsequent studies.
The plant hormone GA promotes chloroplast biogenesis by controlling the expansion of mesophyll cells. The levels of transcription of the genes associated with chloroplast division were also significantly reduced in GA-insensitive mutants (Jiang, Li, et al., 2012). Physiological and transcriptome analysis in this study indicated that DW-B was deficient in GA signal transduction. In addition, DW-B has the phenomenon of repetition. The relationship between the insensitivity of GA signal transduction and the DW-B albinism phenotype merits more study in the future. In another study, we discussed the correlation of grain color. In the genetic analysis, we found that there was some linkage between blue grain and the return of white. The differential gene that we found, hemD, and another gene that controls blue grains, both occur on chromosome 4D. The specific relationship between them merits further research to explain the specificity of our material.
Therefore, as a new dominant semi-dwarf mutant, DW-B is characterized by GA insensitivity-dwarfing, albinism, and blue grain. Further gene cloning and functional characterization will help to dissect the DW-B mediated network control of plant height and other developmental processes.