The PEAPOD Pathway and Its Potential To Improve Crop Yield

The TIFY proteins PEAPOD (PPD)1 and PPD2 recruit KINASE-INDUCIBLE DOMAIN INTERACTING PROTEIN (KIX)8, KIX9, and NOVEL INTERACTOR OF JAZ to form repressor complexes that participate in the transcriptional machinery based on their binding partners. STERILE APETALA (SAP)-mediated proteasome-dependent degradation regulates the abundance of PPD and KIX proteins. The PPD/KIX/SAP module is widely conserved among higher plant species (excluding monocot grasses) and regulates leaf, flower, fruit, and seed development in several crop species of agricultural importance. Emerging evidence suggests that the PPD pathway has a wider role in controlling cell proliferation and developmental plasticity in a tissue-, developmental state-, and/or environmental context-dependent manner than anticipated originally. A key strategy to increase plant productivity is to improve intrinsic organ growth. Some of the regulatory networks underlying organ growth and development, as well as the interconnections between these networks, are highly conserved. An example of such a growth-regulatory module with a highly conserved role in final organ size and shape determination in eudicot species is the PEAPOD (PPD)/KINASE-INDUCIBLE DOMAIN INTERACTING (KIX)/STERILE APETALA (SAP) module. We review the proteins constituting the PPD pathway and their roles in different plant developmental processes, and explore options for future research. We also speculate on strategies to exploit knowledge about the PPD pathway for targeted yield improvement to engineer crop traits of agronomic interest, such as leaf, fruit, and seed size. A key strategy to increase plant productivity is to improve intrinsic organ growth. Some of the regulatory networks underlying organ growth and development, as well as the interconnections between these networks, are highly conserved. An example of such a growth-regulatory module with a highly conserved role in final organ size and shape determination in eudicot species is the PEAPOD (PPD)/KINASE-INDUCIBLE DOMAIN INTERACTING (KIX)/STERILE APETALA (SAP) module. We review the proteins constituting the PPD pathway and their roles in different plant developmental processes, and explore options for future research. We also speculate on strategies to exploit knowledge about the PPD pathway for targeted yield improvement to engineer crop traits of agronomic interest, such as leaf, fruit, and seed size.