Abstract
The MADS-domain transcription factor SEEDSTICK (STK) controls several aspects of plant reproduction. STK is co-expressed with CESTA (CES), a basic Helix-Loop-Helix (bHLH) transcription factor-encoding gene. CES was reported to control redundantly with the brassinosteroid positive signaling factors BRASSINOSTEROID ENHANCED EXPRESSION1 (BEE1) and BEE3 the development of the transmitting tract. Combining the stk ces-4 mutants led to a reduction in ovule fertilization due to a defect in carpel fusion which, caused the formation of holes at the center of the septum where the transmitting tract differentiates. Combining the stk mutant with the bee1 bee3 ces-4 triple mutant showed an increased number of unfertilized ovules and septum defects. The transcriptome profile of this quadruple mutant revealed a small subset of differentially expressed genes which are mainly involved in cell death, extracellular matrix and cell wall development. Our data evidence a regulatory gene network controlling transmitting tract development regulated directly or indirectly by a STK-CES containing complex and reveal new insights in the regulation of transmitting tract development by bHLH and MADS-domain transcription factors.
Highlights
The plant life cycle in Angiosperms is characterized by the alternation of diploid sporophyte and haploid gametophyte generations
Since STK is expressed during female reproductive organ development (Pinyopich et al, 2003; Mizzotti et al, 2014; Herrera-Ubaldo et al, 2019; Di Marzo et al, 2020), we investigated in more detail the spatiotemporal expression pattern of CES during pistil, ovule and seed development
Analysis of the pCES::GUS plants confirmed the in situ data (Figures 1G–I) and these experiments showed that STK and CES partially overlap in their expression patterns during ovule and transmitting tract development (Pinyopich et al, 2003; Crawford and Yanofsky, 2011; Poppenberger et al, 2011; Herrera-Ubaldo et al, 2019)
Summary
The plant life cycle in Angiosperms is characterized by the alternation of diploid sporophyte and haploid gametophyte generations. The sporophyte produces spores, which develop into gametophytes. Sexual reproduction requires the delivery of sperm nuclei, via the pollen tube, to the embryo sac, where fertilization occurs, and the new diploid sporophyte is formed. The growing of the pollen tube through the female reproductive organ tissues in Angiosperms is a crucial step in plant sexual reproduction. The stigma is connected by the style to the ovary, in MADS-bHLH Regulation of Transmitting Tract which lodge the ovules. At the center of the septum, as in the style, the transmitting tract tissue develops. Pollen tubes must travel through several distinct tissues before reaching ovules, including the stigma and the transmitting tract both in the style and in the septum (Lord and Russell, 2002; Roeder and Yanofsky, 2006)
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