Seed Embryo Development Is Regulated via an AN3-MINI3 Gene Cascade.

Lai-Sheng Meng,Yi-Bo Wang,Gary J Loake,Ji-Hong Jiang

doi:10.3389/fpls.2016.01645

Abstract

In agriculture, seed mass is one of the most important components related to seed yield. MINISEED3 (MINI3) which encodes the transcriptional activator WRKY10, is thought to be a pivotal regulator of seed mass. In Arabidopsis SHORT HYPOCOTYL UNDER BLUE1 (SHB1) associates with the promoter of MINI3, regulating embryo cell proliferation (both cell division and elongation), which, in turn, modulates seed mass. Furthermore, the recruitment of SHB1 via MINI3 to both its cognate promoter and that of IKU2 implies a two-step amplification for countering the low expression level of IKU2, which is thought to function as a molecular switch for seed cavity enlargement. However, it is largely unknown how embryo cell proliferation, which encompasses both cell division and elongation, is regulated by SHB1 and MINI3 function. Here, we show that a loss of function mutation within the transcriptional coactivator ANGUSTIFOLIA3 (AN3), increases seed mass. Further, AN3 associates with the MINI3 promoter in vivo. Genetic evidence indicates that the absence of MINI3 function suppresses the decrease of cell number observed in an3-4 mutants by regulating cell division and in turn inhibits increased cell size of the an3-4 line by controlling cell elongation. Thus, seed embryo development is modulated via an AN3-MINI3 gene cascade. This regulatory model provides a deeper understanding of seed mass regulation, which may in turn lead to increased crop yields.

Highlights

ANGUSTIFOLIA3 (AN3)/GRF-INTERACTING FACTOR1, encodes a homolog of the human transcription coactivator, synovial sarcoma translocation protein (SYT) (Horiguchi et al, 2005)
Expression levels in the developing siliques of SHORT HYPOCOTYL UNDER BLUE1 (SHB1), MINI3, IKU2, and AP2 did not significantly differ between wild-type and grf1 mutant plants (Figure 5A). These results suggest that, at least, AN3/GIF1 might act as a cofactor and interact with one or more unknown proteins that might function as specific transcription factors to regulate MINI3 transcription during seed development
Doublemutant analyses revealed that the effect of an3 on seed mass was largely dependent on MINI3 function (Figure 7)

Summary

INTRODUCTION

ANGUSTIFOLIA3 (AN3)/GRF-INTERACTING FACTOR1, encodes a homolog of the human transcription coactivator, synovial sarcoma translocation protein (SYT) (Horiguchi et al, 2005). A triple mutant of the three cytokinin receptors produces twice the seed mass as the corresponding wild-type line In this context, it has been proposed that cytokinin might regulate embryo mass through a maternal and/or endosperm based mechanism (Hutchison et al, 2006; Riefler et al, 2006). The gain-of-function mutant, SHORT HYPOCOTYL UNDER BLUE 1 (SHB1), exhibits a large seed mass as a result of increased cell number and enhanced cell size (Zhou et al, 2009). ABI5-SHB1-MINI3-IKU1 forms a gene cascade that negatively controls embryo cell proliferation and by extension seed mass. It is largely unknown how embryo cell division and elongation is fine-tuned and how in detail seed mass is regulated. Our proposed model provides a greater understanding of seed mass regulation, which may in turn help guide approaches to increase crop yields

MATERIALS AND METHODS

RESULTS

Findings

DISCUSSION