Autonomous and non‐autonomous functions of the maize Shohai1 gene, encoding a RWP‐RK putative transcription factor, in regulation of embryo and endosperm development

Abstract

In plants, establishment of the basic body plan during embryogenesis involves complex processes of axis formation, cell fate specification and organ differentiation. While molecular mechanisms of embryogenesis have been well studied in the eudicot Arabidopsis, only a small number of genes regulating embryogenesis has been identified in grass species. Here, we show that a RKD-type RWP-RK transcription factor encoded by Shohai1 (Shai1) is indispensable for embryo and endosperm development in maize. Loss of Shai1 function causes variable morphological defects in the embryo including small scutellum, shoot axis bifurcation and arrest during early organogenesis. Analysis of molecular markers in mutant embryos reveals disturbed patterning of gene expression and altered polar auxin transport. In contrast with typical embryo-defective (emb) mutants that expose a vacant embryo pocket in the endosperm, the endosperm of shai1 kernels conforms to the varied size and shape of the embryo. Furthermore, genetic analysis confirms that Shai1 is required for autonomous formation of the embryo pocket in endosperm of emb mutants. Analyses of genetic mosaic kernels generated by B-A translocation revealed that expression of Shai1 in the endosperm could partially rescue a shai1 mutant embryo and suggested that Shai1 is involved in non-cell autonomous signaling from endosperm that supports normal embryo growth. Taken together, we propose that the Shai1 gene functions in regulating embryonic patterning during grass embryogenesis partly by endosperm-to-embryo interaction.

Maize biology: From functional genomics to breeding application

“…Mutation of OS1 results in unbalanced nutrient allocation between endosperm and embryo in maize kernels. A similar finding was also recently reported for the same gene (Mimura et al 2018).…”

“…Mutation of OS1 results in unbalanced nutrient allocation between endosperm and embryo in maize kernels. A similar finding was also recently reported for the same gene (Mimura et al ). Dek42 is a new gene, encoding an RRM_RBM48 type RNA binding protein, and mainly functions in intron‐alternative splicing particularly for the U12‐type introns (Zuo et al ).…”

Intra-Kernel Reallocation of Proteins in Maize Depends on VP1-Mediated Scutellum Development and Nutrient Assimilation

“…The most widely used is maize B-A chromosome translocation, which is able to produce a genetically nonconcordant endosperm and embryo in one kernel (Sheridan and Neuffer, 1980;Beckett, 1994). Utilizing this approach, one can observe a defective embryo rescued by a normal endosperm, indicating that a few genes expressed in the endosperm nonautonomously modulate embryo development and that normal embryo development requires a functional endosperm (Fouquet et al, 2011;Mimura et al, 2018). The second approach is by means of the rare heterofertilization phenomenon, in which the genetic relatedness between the endosperm and embryo influences embryo development (Wu et al, 2013).…”

“…By contrast, embryo development relies on a functional endosperm, and severe impairment during early endosperm development usually leads to nonviable or small embryos (Kang et al, 2008;Sosso et al, 2015). Some defectiveembryo mutations can be rescued by a wild-type endosperm via maize B-A chromosome translocations and even by in vivo culture (Sheridan and Neuffer, 1980;Fouquet et al, 2011;Mimura et al, 2018). Thus, impaired nutrient transfer and signal communication between the endosperm and embryo, as well as homozygous mutations of the embryo, can be responsible for defects manifest in the embryo.…”

Transcriptomics at maize embryo/endosperm interfaces identify a novel transcriptionally distinct endosperm sub-domain adjacent to the embryo scutellum (EAS)

“…Our results suggest that EAS-specific gene expression could be a result of several independent factors, some of which could originate from the endosperm, and others from the embryo. The mechanisms involved in embryo cavity formation remain elusive, although a recent study showed that the SHOHAI1 protein is required in the endosperm for the formation of the embryo cavity (Mimura et al, 2018).…”