Abstract
Seed formation is a pivotal process in plant reproduction and dispersal. It begins with megagametophyte development in the ovule, followed by fertilization and subsequently coordinated development of embryo, endosperm, and maternal seed coat. Two closely related MADS-box genes, SHATTERPROOF 1 and 2 (SHP1 and SHP2) are involved in specifying ovule integument identity in Arabidopsis thaliana. The MADS box gene ARABIDOPSIS BSISTER (ABS or TT16) is required, together with SEEDSTICK (STK) for the formation of endothelium, part of the seed coat and innermost tissue layer formed by the maternal plant. Little is known about the genetic interaction of SHP1 and SHP2 with ABS and the coordination of endosperm and seed coat development. In this work, mutant and expression analysis shed light on this aspect of concerted development. Triple tt16 shp1 shp2 mutants produce malformed seedlings, seed coat formation defects, fewer seeds, and mucilage reduction. While shp1 shp2 mutants fail to coordinate the timely development of ovules, tt16 mutants show less peripheral endosperm after fertilization. Failure in coordinated division of the innermost integument layer in early ovule stages leads to inner seed coat defects in tt16 and tt16 shp1 shp2 triple mutant seeds. An antagonistic action of ABS and SHP1/SHP2 is observed in inner seed coat layer formation. Expression analysis also indicates that ABS represses SHP1, SHP2, and FRUITFUL expression. Our work shows that the evolutionary conserved Bsister genes are required not only for endothelium but also for endosperm development and genetically interact with SHP1 and SHP2 in a partially antagonistic manner.
Highlights
For seed setting, most angiosperms go through a double fertilization process, whereby two sperm cells released from a pollen tube fuse with the egg cell and the central cell within the female gametophyte
We produced the triple mutant tt16-1 shp1-1 shp2-1 to assess if ARABIDOPSIS BSISTER gene (ABS) genetically interacts with other MADS-box genes, such as SHP1 and SHP2 which share their domain of expression at least in part with ABS [38, 39]
First we observed the viability of the seedlings for the wild type Ws-4 and Col-0 and mutant seeds which detached from the fruit since the seeds were sieved after harvesting
Summary
Most angiosperms go through a double fertilization process, whereby two sperm cells released from a pollen tube fuse with the egg cell and the central cell within the female gametophyte. These later develop into a diploid embryo and the triploid endosperm constituting the seed which is surrounded by the seed coat originating from the maternal integuments of the ovule [1, 2, 3]. Several studies indicated that proper endosperm development, nuclear division and cellularization are essential for the success of viable seed setting [7]. Several genes, including MADSbox transcription factor encoding genes, have been implicated in the ovule integument and seed endosperm development [12, 13, 14, 15, 16, 17, 7, 18]
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