Abstract
Seed size is a key agronomic trait that greatly determines plant yield. Elucidating the molecular mechanism underlying seed size regulation is also an important question in developmental biology. Here, we show that the KIX-PPD-MYC-GIF1 pathway plays a crucial role in seed size control in Arabidopsis thaliana. Disruption of KIX8/9 and PPD1/2 causes large seeds due to increased cell proliferation and cell elongation in the integuments. KIX8/9 and PPD1/2 interact with transcription factors MYC3/4 to form the KIX-PPD-MYC complex in Arabidopsis. The KIX-PPD-MYC complex associates with the typical G-box sequence in the promoter of GRF-INTERACTING FACTOR 1 (GIF1), which promotes seed growth, and represses its expression. Genetic analyses support that KIX8/9, PPD1/2, MYC3/4, and GIF1 function in a common pathway to control seed size. Thus, our results reveal a genetic and molecular mechanism by which the transcription factors MYC3/4 recruit KIX8/9 and PPD1/2 to the promoter of GIF1 and repress its expression, thereby determining seed size in Arabidopsis.
Highlights
Seed size is a key agronomic trait that greatly determines plant yield
We found that PPD1 and PPD2 interacted with MYC3 and MYC4 (Fig. 2a), but not with MYC2 and other transcription factors (Supplementary Fig. 4)
We previously reported the STERILE APETALA (SAP)-KIX-PPD signalling pathway has an important role in leaf size control[22,23], and performed the RNAseq analysis using the first pair of leaves of 9-day-old myc[3] myc[4] and ppd[1,2] ppd2-cr seedlings. 149 genes with significantly changed expression were found in both myc[3] myc[4] and ppd[1,2] ppd2-cr plants (Supplementary Data 1)
Summary
Seed size is a key agronomic trait that greatly determines plant yield. Elucidating the molecular mechanism underlying seed size regulation is an important question in developmental biology. The KIX-PPD-MYC complex associates with the typical G-box sequence in the promoter of GRF-INTERACTING FACTOR 1 (GIF1), which promotes seed growth, and represses its expression. Our results reveal a genetic and molecular mechanism by which the transcription factors MYC3/4 recruit KIX8/9 and PPD1/2 to the promoter of GIF1 and repress its expression, thereby determining seed size in Arabidopsis. PPD1/2 interact with KINASE-INDUCIBLE DOMAIN INTERACTING 8/9 (KIX8/9) and TOPLESS (TPL) to form a repressor protein complex, which controls the leaf development by influencing the expression of cell division-related genes[21,22]. We find that the KIX-PPD complex controls maternal integument development and influences seed size by regulating cell proliferation and growth. Our results reveal a genetic and molecular mechanism by which the transcriptional repression of GIF1 by the KIX-PPD-MYC complex regulates seed size in Arabidopsis
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