A novel semi-dominant allele of the transmembrane NAC transcription factor ZmNTL2 reduces the size of multiple maize organs

Maize plant architecture influences planting density and, in turn, grain yield. Most of the plant architecture-related traits can be described as organ size. We describe a miniature maize mutant, Tiny plant 4 (Tip4), which exhibits reduced size of multiple organs and exhibits a semi-dominant monofactorial inheritance characteristic. Positional cloning confirmed that a 4-bp deletion in the NAC TF with transmembrane motif 1-Like (NTL) gene ZmNTL2, denoted as ZmNTL2^Δ, confers the Tip4 mutation. qRT-PCR showed that ZmNTL2 was expressed in all tested tissues. ZmNTL2 functions as a transcriptional activator and is located in both the nucleus and biomembranes. The mutation does not affect the mRNA abundance of ZmNTL2 locus, but it does result in the loss of transmembrane domain and confines the ZmNTL2^Δ protein to the nucleus. Knocking out ZmNTL2 has no effect on maize organ size development, indicating that the 4-bp deletion might be a gain-of-function mutation in organ size regulation. Combining transcriptome sequencing with cytokinin and auxin content determination suggests that the decreased organ size may be possibly mediated by changes in hormone homeostasis.