THE STORY OF HaHB11: HOW TO BE A CROP AND NOT DIE IN THE ATTEMPT

RAINERI, JESICA; CHAN, RAQUEL L; CARABALLO LUCIANO; OTEGUI, MARÍA E.

Congreso; Congreso Conjunto SAIB-SAMIGE 2020; 2020

HaHB11 is a sunflower transcription factor belonging to de HD-Zip I family. Its ectopic and constitutive expression in Arabidopsis generates increased biomass, seed yield, and waterlogging tolerance, compared with wild type plants. With this proof of concept, we transformed maize with the 35S:HaHB11 construct and evaluated the phenotype of two independent events (E2 and E3), using as control null segregant plants. We have previously reported that maize HaHB11 lines (in B73 background) exhibited better performance than control plants in greenhouse and field assays. To know if transgenic plants were also more tolerant to abiotic stress, particularly waterlogging, we carried out waterlogging assays subjecting plants to such treatment for two weeks and then allowing them to recover. Transgenic plants showed longer roots with more xylem vessels, larger leaf-area and conductivity than control plants during the treatment. After recovery, HaHB11 plants developed larger leaves with delayed senescence and more nodal roots than controls. This phenotype allowed the transgenic plants to fill more grains and conducting to increased yield. We made this evaluation in the greenhouse and field assay with similar results.These results encouraged us to generate maize hybrids, more similar to commercial material. We performed crosses with B73 lines (transgenic and control plants) and the public line Mo17. HaHB11 maize hybrids in the greenhouse showed an improved phenotype in control or waterlogging conditions, expressed as delayed senescence, larger leaf area, a higher number of grains, and yield compared to controls in both conditions. Moreover, differential gene expression was detected between genotypes. After evaluating the phenotype in the greenhouse, we decided to perform field assays. The design of the plots included B73 lines and hybrids, with the corresponding controls. Unfortunately, the assay was seriously affected by a strong storm eleven days after anthesis. All the plants lost their leaves in the critical period of grain set and filling. Surprisingly, transgenic plants set a higher number of grains and showed higher yield than controls. After this serendipitous discovery, we carried out controlled defoliation assays in the greenhouse and field. In all cases, transgenic plants (both lines and hybrid background) showed increased grain number than control plants.These results strongly support that HaHB11 could be used as a biotechnological tool to improve maize plants both in standard conditions and to deal with waterlogging and defoliation.