A novel FLOURY ENDOSPERM2 (FLO2)-interacting protein, is involved in maintaining fertility and seed quality in rice

Abstract

Crop plants accumulate a large amount of storage starch and storage proteins in the endosperm. Genes involved in the biosynthesis of these substances work in concert during development of the rice endosperm. The rice flo2 mutant produces aberrant seeds with reduced grain quality. FLOURRY ENDOSPERM 2 (FLO2), the causative gene of the flo2 mutant, is considered to be a regulatory protein that controls the biosynthesis of seed storage substances. FLO2 contains tetratricopeptide repeat (TPR) motifs that may mediate protein-protein interactions. In this study, we identified the protein that interacts with the TPR motif of FLO2. We generated a transformant that produced the FLAG-tagged fusion FLO2 protein in the flo2 mutant and used this in the shotgun proteomic analysis. A protein, which we named FLOC1, interacted with FLO2. In vitro pull-down assays indicated that the TPR motif was involved in this interaction. A knockdown transformant of FLOC1 showed significantly reducted fertility and generation of seeds with abnormal features. These findings suggest that FLOC1 is involved not only in seed fertility but also in seed quality. These phenotypes were also observed on the RNAi transformants of the flo2 mutant although the effect of the flo2 mutation remained. these findings imply that there is a difference in the functions of FLO2 and FLOC1 although both of appear to be involved in the control of seed quality during seed formation.

Orchestrating seed storage protein and starch accumulation toward overcoming yield–quality trade‐off in cereal crops

“…FLO2 overexpression enhances the expression of starch enzyme (AGPL1, AGPL4 and GBSSI) and SSP genes (such as GluA1, glutelin A1, and 11Sglobulin) genes, the consequence of which was increased amylose content, grain weight and grain size, suggesting that it plays a pivotal regulatory role in rice yield and starch quality. FLOC1, an interactor of FLO2, also participates in the control of seed quality during grain filling (Suzuki et al, 2020). Liu et al (2023b) recently characterized an "Oat-like rice" mutant with poor grain quality, including abnormal morphology, chalky endosperm, loose arrangement of starch granules, higher GPC and lower starch content.…”

“…FLO2 overexpression enhances the expression of starch enzyme ( AGPL1 , AGPL4 and GBSSI ) and SSP genes (such as GluA1, glutelin A1 , and 11S‐globulin ) genes, the consequence of which was increased amylose content, grain weight and grain size, suggesting that it plays a pivotal regulatory role in rice yield and starch quality. FLOC1, an interactor of FLO2, also participates in the control of seed quality during grain filling (Suzuki et al, 2020).…”

Regulators of Starch Biosynthesis in Cereal Crops

“…One basic helix–loop–helix (bHLH) protein may interact with FLO2 to modulate the expression of starch biosynthesis-associated nuclear genes (SBANGs) [ 75 ]. Subsequently, the FLO2-interacting cupin domain protein 1 (FLOC1) was reported to interact with the TPR motif of FLO2 to maintain fertility and seed quality in rice [ 77 ], even though they are supposed to have different functions.…”

Generation of new rice germplasms with low amylose content by CRISPR/CAS9-targeted mutagenesis of the FLOURY ENDOSPERM 2 gene

“…FLOURY ENDOSPERM 2 ( FLO2 ), a member of a conserved gene family in plants, encodes a tetratricopeptide repeat domain (TPR)-containing protein located in the nucleus ( She et al., 2010 ; Wu et al., 2015 ; Kolli et al., 2019 ; Suzuki et al., 2020 ). It has been reported that FLOURY ENDOSPERM 2 could not only modulate the expression of starch synthesis-related genes including OsAGPL2, OsAGPS2b, OsGBSSI, OsBEI, OsBEIIb, OsISA1 and OsPUL , but also directly impact on the amylose biosynthesis by manipulating the splicing efficiency of Wx pre-mRNA ( Wu et al., 2015 ; Cai et al., 2022 ; Feng et al., 2022 ; Sreenivasulu et al., 2022 ).…”

“…Previous studies have shown that flo2 , the loss-of-function mutant of FLOURY ENDOSPERM 2 , produced two distinct phenotypes, one with white and floury endosperm, and the other with dull grain ( She et al., 2010 ; Hunt et al., 2013 ; Boehlein et al., 2018 ). In the former, starch granules were small, spherical and loosely packed with large air space ( Malinova et al., 2017 ; Jiang et al., 2018 ; Suzuki et al., 2020 ). The FLOURY ENDOSPERM 2 also affected grain size as demonstrated by both overexpression and null mutation approaches ( She et al., 2010 ; Zhang et al., 2013 ).…”