SbNAC22 coordinates starch biosynthesis in sorghum grain by regulating pathway related functional genes

Highlights 1 A NAC-family transcription factor of SbNAC22 with self-activating was profiled to regulate the transcription of multiple starch biosynthesis related genes by binding to the NAC-specific cis -elements. Over-expressed SbNAC22 in rice line of Zhonghua 11 caused enhanced grain length and weight, as well as significantly increased total starch content in the grains. Integrated results of both sorghum and rice implied that SbNAC22 could transactivate SbAGPLS1, SbGBSSI, SbSSI , and suppress SbISA1 , to regulate starch biosynthesis and accumulation in developing sorghum grains. Starch, the predominant component in sorghum grains and a key component for utilization, is primarily regulated by spatiotemporally specific starch biosynthesis-related genes (SBRGs) with poorly characterized transcriptional mechanisms. This study elucidates the functional role of the NAC-type transcription factor (TF) SbNAC22 in starch biosynthesis in sorghum grains. SbNAC22 exhibits preferential expression levels in developing grains and demonstrates co-expression trends with multiple sorghum SBRGs. SbNAC22 possesses nuclear targeting, autoactivation activity, and intrinsic activity domain. The integrated results of DAP-seq, dual-luciferase analysis, and EMSA imply that SbNAC22 could bind to the conserved motif of 5‘-CACGCAA-3‘, influencing the promoter activities of the corresponding SBRGs. Transient overexpression assays revealed that SbNAC22 can also upregulate critical SBRGs of SbAGPLS1, SbGBSSI , and SbSSI , while suppress SbISA1 in sorghum. Heterologous expression in rice further demonstrates the conserved regulatory capacity of SbNAC22, elevating transcript levels of rice SBRGs, enhancing grain length and weight, and significantly increasing the starch content in rice grains. The findings of this study identify SbNAC22 as a key transcriptional regulator that orchestrates starch biosynthesis by differentially activating and repressing SBRGs, positioning SbNAC22 as a prime target for novel molecular breeding strategies designed to enhance both grain yield and quality in sorghum.