Comparison of Transcript Profiles in Wild‐Type and o2 Maize Endosperm in Different Genetic Backgrounds

Abstract

Mutations in the Opaque2 (O2) gene of maize (Zea mays L.) improve the nutritional value of maize by reducing the level of zeins in the kernel. The phenotype of o2 grain is controlled by many modifier genes and is therefore strongly dependent on genetic background. We propose two hypotheses to explain differences in phenotypic severity in different genetic backgrounds: (i) Specific genes are differentially (o2 vs. wild‐type) expressed only in certain genotypes, and (ii) A set of genes are differentially expressed in all backgrounds, but the degree of differential expression differs in different backgrounds. To determine the extent to which these two hypotheses contribute to determining the severity of o2 in different genetic backgrounds, we identified transcripts likely to be differentially expressed in several genetic backgrounds by transcript profile comparison of endosperm RNA pools from eight o2 inbred lines and their wild‐type counterparts. The inbred line B46 was identified as having severe o2 phenotypes while the line M14 was identified as having minimal o2 phenotypes. The degree of wild‐type vs. o2 differential expression of transcripts was determined for these two lines. We found that most genes that are downregulated by o2 tend to be differentially expressed to a greater degree in B46 than in M14, while upregulated genes tend to be more highly differentially expressed in one genetic background or the other. Thus, hypothesis one functions more prominently for upregulated genes while hypothesis two functions most prominently for downregulated genes.

Kernel lysine content does not increase in some maize opaque2 mutants

“…These experiments showed that the lysine content of most of the o2 NILs in this study increased significantly, compared with that of their respective recurrent parents, indicating that the inbred lines CA335 and CA339 were effective donors of the o2 allele coding for a defective OPAQUE2 polypeptide. The present study demonstrated that lysine content varies greatly in different o2 NILs and proved that the phenotypic effects of the o2 mutant are dependent upon genetic backgrounds; these data agreed with previous studies demonstrating that o2 phenotypes were background-dependent (Moro et al 1996;Jia et al 2007). All previous studies showed that increased lysine content could be attributed to o2 mutant alleles and that lysine content varied according to genetic background (Moro et al 1996;Jia et al 2007).…”

“…The present study demonstrated that lysine content varies greatly in different o2 NILs and proved that the phenotypic effects of the o2 mutant are dependent upon genetic backgrounds; these data agreed with previous studies demonstrating that o2 phenotypes were background-dependent (Moro et al 1996;Jia et al 2007). All previous studies showed that increased lysine content could be attributed to o2 mutant alleles and that lysine content varied according to genetic background (Moro et al 1996;Jia et al 2007). However, the present results showed that lysine content did not increase in some maize NILs carrying an o2 allele and that there was no significant difference in kernel characters between some recurrent parents (Dan598 and Liao2345) and their respective o2 NILs (Dan598o2 and Liao2345o2).…”

“…All previous studies showed that the o2 mutation increases lysine content in maize concomitant with the reduction of zein synthesis (i.e., the increase of non-zein synthesis) (Habben et al 1993;Hunter et al 2002), but that the degree of increase in lysine content in the o2 mutant depended on the genetic background (Moro et al 1996;Jia et al 2007). Ciceri et al (2000) reported that a-zein pattern was not altered in some maize lines after the o2 mutation was introgressed.…”

Genome-Wide Characterization ofcis-Acting DNA Targets Reveals the Transcriptional Regulatory Framework ofOpaque2in Maize

“…LKR/SDH, which encodes a bifunctional enzyme involved in Lys catabolism (Kemper et al, 1999), is also regulated by O2. Gene expression profiling analysis of o2 mutants revealed that O2 regulates transcription of many genes involved in a variety of pathways (Frizzi et al, 2010;Hartings et al, 2011;Hunter et al, 2002;Jia et al, 2007;Jia et al, 2013), which is consistent with the described pleiotropic effects of the mutant.…”

“…To provide a more detailed understanding of O2-regulated gene expression, profiling studies based on microarray analysis were performed that revealed multiple DEGs in o2 endosperm (Hunter et al, 2002;Jia et al, 2007;Frizzi et al, 2010;Hartings et al, 2011;Jia et al, 2013). These studies showed that, along with 22-kD a-zeins and the 14-kD b-zein, a number of other zein genes, e.g., 19-kD a-zeins and the 10-kD d-zein, also showed decreased transcription.…”