Expression of Maize MADS Transcription Factor Negatively Modulates Starch Accumulation in Rice Endosperm.

As major component in cereals grains, starch has been one of the most important carbohydrate consumed by a majority of world's population. However, the molecular mechanism for regulation of biosynthesis of starch remains elusive. In the present study, , encoding a MADS-type transcription factor, was modestly characterized from maize inbred line B73. exhibited high expression level in endosperm at 10 days after pollination (DAP) and peaked in endosperm at 20 DAP, indicating that was preferentially expressed in maize endosperm during active starch synthesis. Transient expression of in tobacco leaf revealed that ZmES22 protein located in nucleus. No transactivation activity could be detected for ZmES22 protein via yeast one-hybrid assay. Transformation of overexpressing plasmid 35S:: into rice remarkedly reduced 1000-grain weight as well as the total starch content, while the soluble sugar was significantly higher in transgenic rice lines. Moreover, overexpressing reduced fractions of long branched starch. Scanning electron microscopy images of transverse sections of rice grains revealed that altered expression of also changed the morphology of starch granule from densely packed, polyhedral starch granules into loosely packed, spherical granules with larger spaces. Furthermore, RNA-seq results indicated that overexpressing could significantly influence mRNA expression levels of numerous key regulatory genes in starch synthesis pathway. Y1H assay illustrated that ZmES22 protein could bind to the promoter region of and downregulate its mRNA expression during rice grain filling stages. These findings suggest that was a novel regulator during starch synthesis process in rice endosperm.