OsMADS1 Regulates Grain Quality, Gene Expressions, and Regulatory Networks of Starch and Storage Protein Metabolisms in Rice

Abstract

OsMADS1 plays a vital role in regulating floret development and grain shape, but whether it regulates rice grain quality still remains largely unknown. Therefore, we used comprehensive molecular genetics, plant biotechnology, and functional omics approaches, including phenotyping, mapping-by-sequencing, target gene seed-specific RNAi, transgenic experiments, and transcriptomic profiling to answer this biological and molecular question. Here, we report the characterization of the ‘Oat-like rice’ mutant, with poor grain quality, including chalky endosperms, abnormal morphology and loose arrangement of starch granules, and lower starch content but higher protein content in grains. The poor grain quality of Oat-like rice was found to be caused by the mutated OsMADS1Olr allele through mapping-by-sequencing analysis and transgenic experiments. OsMADS1 protein is highly expressed in florets and developing seeds. Both OsMADS1-eGFP and OsMADS1Olr-eGFP fusion proteins are localized in the nucleus. Moreover, seed-specific RNAi of OsMADS1 also caused decreased grain quality in transgenic lines, such as the Oat-like rice. Further transcriptomic profiling between Oat-like rice and Nipponbare grains revealed that OsMADS1 regulates gene expressions and regulatory networks of starch and storage protein metabolisms in rice grains, hereafter regulating rice quality. In conclusion, our results not only reveal the crucial role and preliminary mechanism of OsMADS1 in regulating rice grain quality but also highlight the application potentials of OsMADS1 and the target gene seed-specific RNAi system in improving rice grain quality by molecular breeding.

Compensatory Modulation of Seed Storage Protein Synthesis and Alteration of Starch Accumulation by Selective Editing of 13 kDa Prolamin Genes by CRISPR-Cas9 in Rice

“…Recently, it has been reported that TFs spontaneously regulate starch and SSP synthesis during seed development in rice [ 12 ], including OsbZIP58 [ 14 , 60 ], Nhd1 [ 61 ], OsNAC20 [ 15 ], OsNAC26 [ 15 ], FLO2 [ 62 ], and OsMADS1 [ 63 ]. OsbZIP58 activates the expression of starch synthesis-related genes ( OsAGPL3 , GBSSI , SSIIa , SBE1 , BEIIb , and ISA2 ) by directly binding their promoters [ 60 ] and interacts with rice prolamin box binding factor, activating the expression of SSP genes ( GluA1 ~ 3 , GluB1 , GluD1 , and 10/13/16 kDa prolamins ) [ 14 ].…”

“…The function-loss mutation of the FLOURY ENDOSPERM2 ( FLO2 ) gene caused a decrease in grain size and starch content by reducing the expression of starch and SSP-related genes, while its overexpression resulted in an increase in amylose content and grain weight/size by enhancing the expression of starch ( AGPL1 , AGPL4, and GBSSI ) and SSP genes ( GluA1 and globulin ) [ 62 ]. Moreover, Oat-like rice (Olr), which was generated by a mutated OsMADS1 allele, showed a loose arrangement of starch granules, and reduced starch content but increased SSP content [ 63 ]. The results indicate that the regulatory mechanisms of SSP and starch synthesis are coupled by TFs, and investigating novel TFs and understanding their regulatory networks are crucial factors in improving seed quality and yield.…”

Molecular Research in Rice

“…The investigation of Liu et al [ 7 ] revealed that OsMADS1 regulates grain quality by regulating starch and storage protein metabolism in rice. However, the regulatory mechanism has yet to be elucidated.…”