Ontogeny of the Maize Shoot Apical Meristem

Abstract

The maize (Zea mays) shoot apical meristem (SAM) arises early in embryogenesis and functions during stem cell maintenance and organogenesis to generate all the aboveground organs of the plant. Despite its integral role in maize shoot development, little is known about the molecular mechanisms of SAM initiation. Laser microdissection of apical domains from developing maize embryos and seedlings was combined with RNA sequencing for transcriptomic analyses of SAM ontogeny. Molecular markers of key events during maize embryogenesis are described, and comprehensive transcriptional data from six stages in maize shoot development are generated. Transcriptomic profiling before and after SAM initiation indicates that organogenesis precedes stem cell maintenance in maize; analyses of the first three lateral organs elaborated from maize embryos provides insight into their homology and to the identity of the single maize cotyledon. Compared with the newly initiated SAM, the mature SAM is enriched for transcripts that function in transcriptional regulation, hormonal signaling, and transport. Comparisons of shoot meristems initiating juvenile leaves, adult leaves, and husk leaves illustrate differences in phase-specific (juvenile versus adult) and meristem-specific (SAM versus lateral meristem) transcript accumulation during maize shoot development. This study provides insight into the molecular genetics of SAM initiation and function in maize.

Transcriptomic Analyses Indicate That Maize Ligule Development Recapitulates Gene Expression Patterns That Occur during Lateral Organ Initiation

“…The genes brown midrib1, Ran BINDING PROTEIN2 (specific to vascular tissues), and Rubisco small subunit are predicted to be expressed only in subepidermal cell layers (Humphreys and Chapple, 2002;Takacs et al, 2012). In our data sets, these transcripts were not represented in epidermis-only captures or were present at low levels relative to the all-cell-layers captures, thus supporting the accuracy of the captures.…”

“…Microlaser Technologies). RNA extraction and amplification, cDNA library preparation, and Illumina sequencing were performed as described previously (Takacs et al, 2012).…”

Comprehensive Tissue-Specific Transcriptome Analysis Reveals Distinct Regulatory Programs during Early Tomato Fruit Development

“…Thus, sense-strand reads were counted after extending the tomato gene models 1 kb upstream of the translational start site and 1 kb downstream of the translational stop site, to include reads from untranslated region sequences that may not have been annotated. As in previous LCM studies (Takacs et al, 2012), read counts were normalized to the total number of reads mapped (RPM).…”

The Differential Transcription Network between Embryo and Endosperm in the Early Developing Maize Seed

“…So far, transcriptomic analyses have been carried out in maize with pericycle cells of the primary root (Dembinsky et al, 2007), endosperm (Prioul et al, 2008), seedling (Fu et al, 2010), leaf bundle sheath , kernel and leaf meristem (Kakumanu et al, 2012), and shoot apical meristem (Takacs et al, 2012). However, to our knowledge, the genome-wide transcriptional profile of embryo and endosperm by RNA-seq technology in maize has not yet been performed.…”