The SUMOylation is one of the critical regulatory protein modifications and plays a pivotal role in cardiac development and disease.Several cardiac transcription factors aremodified by SUMO,but little is known about the impact of SUMOylation on their function during cardiac development.We used zebrafish model to address the SUMOylation role of GATA5,an essential transcription factor for zebrafish cardiac development.Firstly,we identified GATA5 as SUMO substrate,and lysine 324(K324)and lysine 360(K360)were two major modification sites.Conversion of lysine to arginine of these two sitesdid not affect subcellular localization but transcriptional activityof GATA5.Secondly,in vivo experiments showed wild type(WT)and K324R mutant of gata5 can rescue reduced cardiac precursor and differentiation,while K360R mutant of gata5 mRNA radicallylost this potencyin gata5-morpholino knock-down morphantembryos.Furthermore,in SUMOylationdeficientubc9 mutants,early markers of abnormal expression pattern of cardiac developmentnkx2.5 and mef2cb can be restored by sumo2-gata5fusion,but not byWTgata5.Our studies demonstrated that the SUMOylation of GATA5 was indispensable for early zebrafish cardiac development and revealed potential importance of SUMOylation of transcription factors in cardiac development and disease.