A transposon inserted into HELD1 repressed maize husk leaf blade extension during maize domestication

Husk leaves are the closest photosynthetic organs to the ear, which contribute directly to grain filling and have potential for yield improvement in maize. Teosinte has a long husk extended leaf blade, whereas maize exhibits a reduced or even no husk leaf blade. However, the genetic basis of this transition in the husk leaf during domestication remains unknown. In this study, we identified a major quantitative trait locus (QTL), Husk Extended Leaf Blade 1 (HELD1), corresponding to the tassels replace upper ears1 (tru1) gene. A 133-base pair (bp) Harbinger transposon inserted into the tru1 intron introduces two TEOSINTE BRANCHED 1 (TB1) binding motifs, thereby recruiting TB1 to directly enhance tru1 transcription. Further analyses revealed that TRU1 interacts with the transcription factor ALOG1, which in turn enhances the expression of liguleless2 (lg2), a key regulator of ligule development. Together with brassinosteroid-deficient dwarf1 (brd1) and GA2ox1, these genes set up a regulatory network that defines the ligular-auricular position, controls the leaf blade-to-husk (sheath) ratio in husk and stem leaves, and regulates husk leaf blade length. Population genetic analyses indicate that HELD1 experienced significant human selection, resulting in the transposon insertion becoming the dominant allele in domesticated maize. Additionally, the teosinte HELD1 allele with extended husk leaf blades significantly enhances yield in maize. Our results demonstrate HELD1 is an important regulator of husk and stem leaf architectures, contributing to the ligular-auricular position to adjust the ratio of leaf blade to husk or sheath.