Maize expressing the sunflower transcription factor HaHB11 has improved productivity in controlled and field conditions.

HaHB11 is a sunflower transcription factor from the homeodomain-leucine zipper I family. Transgenic Arabidopsis plants expressing HaHB11 had larger rosettes and improved seed yield. In this work maize plants from hybrid HiII were transformed with 35S:HaHB11, ZmUBI:HaHB11 and ProHaHB11:HaHB11 and then backcrossed to B73 to obtain a more homozygous inbred phenotype. Transgene expression levels were stable at least during three generations. Greenhouse-grown HaHB11 transgenic lines had larger leaf area and delayed senescence than controls, together with increased total biomass (up to 25%) and seed yield (up to 28%). Field trials conducted with T2 and T4 generations indicated that enhanced leaf area (up to 18%), stem diameter (up to 28%) and total biomass (up to 40%) as well as delayed leaf senescence were maintained among transgenic individuals when upscaling from pots in the greenhouse to communal plants in the field. The T4 field-grown transgenic generation had increased light interception and radiation use efficiency as well as seed yield (43-47% for events driven by the 35S promoter). Results suggest that HaHB11 is a promising tool for crop improvement because differential traits observed in the Arabidopsis model plant were preserved in a crop like maize independently of growth conditions and backcross level.