AI Article Synopsis

  • During seed development in Arabidopsis and many dicots, the process involves early endosperm proliferation, creating a large seed cavity which is later filled by embryo growth.
  • Short hypocotyl under BLUE1 (SHB1) boosts endosperm growth and seed size by enhancing expression of key genes MINISEED3 (MINI3) and HAIKU2 (IKU2); mutations in these genes lead to reduced seed size.
  • The regulation of MINI3 and IKU2 by SHB1 is crucial, as SHB1 activates their expression during a specific timeframe after pollination, facilitating endosperm expansion and seed cavity formation.

Article Abstract

Seed development in Arabidopsis and in many dicots involves an early proliferation of the endosperm to form a large embryo sac or seed cavity close to the size of the mature seed, followed by a second phase during which the embryo grows and replaces the endosperm. Short hypocotyl under BLUE1 (SHB1) is a member of the SYG1 protein family in fungi, Caenorhabditis elegans, flies, and mammals. SHB1 gain-of-function enhances endosperm proliferation, increases seed size, and up-regulates the expression of the WRKY transcription factor gene MINISEED3 (MINI3) and the LRR receptor kinase gene HAIKU2 (IKU2). Mutations in either IKU2 or MINI3 retard endosperm proliferation and reduce seed size. However, the molecular mechanisms underlying the establishment of the seed cavity and hence the seed size remain largely unknown. Here, we show that the expression of MINI3 and IKU2 is repressed before fertilization and after 4 days after pollination (DAP), but is activated by SHB1 from 2 to 4 DAP prior to the formation of the seed cavity. SHB1 associates with their promoters but without a recognizable DNA binding motif, and this association is abolished in mini3 mutant. MINI3 binds to W-boxes in, and recruits SHB1 to, its own and IKU2 promoters. Interestingly, SHB1, but not MINI3, activates transcription of pMINI3::GUS or pIKU2::GUS. We reveal a critical developmental switch through the activation of MINI3 expression by SHB1. The recruitment of SHB1 by MINI3 to its own and IKU2 promoters represents a novel two-step amplification to counter the low expression level of IKU2, which is a trigger for endosperm proliferation and seed cavity enlargement.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591269PMC
http://dx.doi.org/10.1371/journal.pgen.1003347DOI Listing

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