Transcriptional repression of GIF1 by the KIX-PPD-MYC repressor complex controls seed size in Arabidopsis

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.

GmKIX8‐1 regulates organ size in soybean and is the causative gene for the major seed weight QTL qSw17‐1

“…S2). Since genetic defects in AtKIX8 are known to result in increased seed and leaf size in Arabidopsis (Gonzalez et al, 2015;Liu et al, 2020), we hypothesized that the GmKIX8-1 deletion is the causative genetic lesion responsible for the mutant phenotypes in K83. Gene expression analysis of leaves…”

“…S2). Since genetic defects in AtKIX8 are known to result in increased seed and leaf size in Arabidopsis (Gonzalez et al ., 2015; Liu et al ., 2020), we hypothesized that the GmKIX8‐1 deletion is the causative genetic lesion responsible for the mutant phenotypes in K83. Gene expression analysis of leaves showed that the expression of GmKIX8‐1 was detected in leaves of wild‐type plants but not in the K83 mutant, further indicating that the GmKIX8‐1 gene was indeed deleted in the mutant (Fig.…”

“…However, as was the case in Arabidopsis AtCYCD3;2 and AtCYCD3;2 (Baekelandt et al ., 2018), these GmCYCD3 genes may still be targets in other soybean tissues and/or developmental stages that were not examined here. In addition to D3‐type cyclins, the PPD/KIX module, in association with the transcription factors MYC3/4, represses the expression of the transcriptional co‐activator GIF1 (Liu et al ., 2020). The KIX‐PPD‐MYC‐GIF1 module was implicated in the control of Arabidopsis seed size by restraining cell proliferation of the outer integument during both ovule and early seed developmental stages (Liu et al ., 2020).…”

“…In addition to D3‐type cyclins, the PPD/KIX module, in association with the transcription factors MYC3/4, represses the expression of the transcriptional co‐activator GIF1 (Liu et al ., 2020). The KIX‐PPD‐MYC‐GIF1 module was implicated in the control of Arabidopsis seed size by restraining cell proliferation of the outer integument during both ovule and early seed developmental stages (Liu et al ., 2020). GIF1 expression was upregulated in Arabidopsis and Medicago harboring mutations in PPD and/or KIX genes (Ge et al ., 2016; Liu et al ., 2020), and in soybean where PPD genes were targeted by microRNA(Ge et al ., 2016).…”

“…The KIX‐PPD‐MYC‐GIF1 module was implicated in the control of Arabidopsis seed size by restraining cell proliferation of the outer integument during both ovule and early seed developmental stages (Liu et al ., 2020). GIF1 expression was upregulated in Arabidopsis and Medicago harboring mutations in PPD and/or KIX genes (Ge et al ., 2016; Liu et al ., 2020), and in soybean where PPD genes were targeted by microRNA(Ge et al ., 2016). Therefore, a similar mechanism involving the PPD‐KIX‐MYC‐GIF1 in seed size control likely also operates in soybean.…”