Yield maintenance under drought: expansive growth and hydraulics also matter in reproductive organs

Yield maintenance under drought in maize (Zea mays) is associatedwith flowering synchrony which requires the rapid extensionof styles and stigma (silks) to be accessible for pollen. Wehave shown that the control of grain set under moderate waterdeficits similar to those in the field result from a developmentalprocess linked to the timing of silk growth, in opposition to thecommon view that abortion is linked to the sugar metabolismin ovaries. A switch to abortion occurs 2-3 days after first silkemergence in water-stressed plants, when silk growth stops simultaneouslyfor all ovary cohorts, and explains abortion rates indifferent treatments, genotypes and positions on the ear. Analysesof transcripts and metabolites indicate that the first molecularevents occur in silks rather than in ovaries, and involve genesaffecting expansive growth rather than sugar metabolism. Sugaravailability is preserved in ovaries until the switch to abortion,and the disruption of carbon metabolism only occurs afterwards.Hence, changes in metabolite contents, transcript amounts andenzyme activities involved in ovary sugar metabolism would bea consequence rather than a cause of the beginning of ovaryabortion. Patterns of silk growth responses to environment sharecommon features with those of leaf growth, with both kineticand genetic evidences. These findings have large consequencesfor breeding drought tolerant maize and for modelling grainyields under drought. Oury et al (2016) Plant Physiology171: 986-996 and 171: 997-1008Turc et al (2016) New Phytologist 212: 377–38