Transcriptome Dynamics of Double Recessive Mutant, o2o2o16o16, Reveals the Transcriptional Mechanisms in the Increase of Its Lysine and Tryptophan Content in Maize

Abstract

In maize, pyramiding of o2 and o16 alleles can greatly improve the nutritional quality of grains. To dissect its molecular mechanism, we created a double recessive mutant line, o2o2o16o16, by introgression of the o2 and o16 alleles into the wild-type maize inbred line, by molecular marker-assisted backcross selection. The kernels (18 day after pollination (DAP), 28 DAP, and 38 DAP) of the o2o2o16o16 mutant and its parent lines were subject to RNA sequencing (RNA-Seq). The RNA-Seq analysis revealed that 59 differentially expressed genes (DEGs) were involved in lysine metabolism and 43 DEGs were involved in tryptophan metabolism. Among them, the genes encoding AK, ASADH, and Dap-F in the lysine synthesis pathway were upregulated at different stages of endosperm development, promoting the synthesis of lysine. Meanwhile, the genes encoding LKR/SDH and L-PO in the lysine degradation pathway were downregulated, inhibiting the degradation of lysine. Moreover, the genes encoding TAA and YUC in the tryptophan metabolic pathway were downregulated, restraining the degradation of tryptophan. Thus, pyramiding o2 and o16 alleles could increase the lysine and tryptophan content in maize. These above results would help to uncover the molecular mechanisms involved in the increase in lysine and the tryptophan content, through the introgression of o2 and o16 alleles into the wild-type maize.

Connections Between Amino Acid Metabolisms in Plants: Lysine as an Example

“…Similar findings were found during the regulation of methionine metabolism (Song et al, 2013). Interestingly, high tryptophan levels were found to be associated with high-lysine plants (Yang et al, 2018;Wang et al, 2019), while Yang et al (2018) revealed that the accumulation of lysine induced the tryptophan synthesis and metabolism in high free lysine transgenic rice (Oryza sativa L.). However, few reports have documented the relationship between metabolism of different amino acid families, highlighting the need for further research.…”

Comparative Transcriptome Analysis Reveals Mechanisms of Folate Accumulation in Maize Grains

“…The kernels of double recessive mutant o2o2o16o16 contained increased Gly as well as reduced Glu and Met. Coincidently, a total of 24 folate-related genes showed significant variation of expression between mutant and wild type, and 21 of them were also found in our WGCNA module analysis, including the key folate genes ADCS, DHNA2, GGH, SHMT7-1, SHMT7-2, and GCST (Tables S3 and S7) [68]. Similarly, studies in tomato and millet (Setaria italica) also demonstrated that folate accumulation in different cultivars was closely related to the genes involved in pteridine branch, ρ-ABA branch, folate degradation, and serine/THF/5-M-THF cycle, such as SiDHNA2, SiGGH, SiSHMT2, SiSHMT3, SiMTHFR, SiAMT (known as GCST), SlDHNA, and SlADCS [25,69].…”

“…Similar connections were also identified between amino acid and folate metabolisms. For instance, O2 and O16 encode the transcription factors of the basic leucine zipper family, and they have been used to improve the amino acid quality of maize grains [68]. The kernels of double recessive mutant o2o2o16o16 contained increased Gly as well as reduced Glu and Met.…”

Dissecting the Regulatory Network of Leaf Premature Senescence in Maize (Zea mays L.) Using Transcriptome Analysis of ZmELS5 Mutant

“…The RT-qPCR was performed using the CFX96 Touch™ Real-Time PCR Detection System (Bio-Rad, Hercules, CA, USA). The Actin gene was used as the endogenous control [54]. The relative expressions of RNAs and targets were calculated using the 2 −ΔΔCt method [55].…”