Involvement of the Ivr2-invertase in the perianth during maize kernel development under water stress

The susceptibility of early developing grain to water stress is a major problem in maize, assimilate shortage being a likely cause for insufficient grain filling. Both cell wall and vacuolar invertases appear to be involved in this failure. To date, most data concern molecular analysis of the Incw2 cell wall invertase expressed in the basal endosperm and its association with the miniature mutation. Here the predominant role, at early post-pollination stage, 4 days after pollination (DAP), of a vacuolar invertase located in the perianth adhering to the kernels is presented. Both Ivr2 mRNA and the corresponding vacuolar invertase activity were strongly reduced by a mild water stress while Incw2 transcripts and the kernel cell wall invertase activity were hardly modified. Hybridisation with an Ivr2 3'UTR-probe strongly suggested that the same gene was expressed in perianth and leaf although its response to water stress was the opposite. In order to check for a perianth specific gene, cloning of genomic Ivr2 DNA was performed. A partial gene covering ca. 80% of the coding region and the specific UTR sequence was obtained. It mapped to a unique locus on chromosome 5 where a QTL for vacuolar invertase activity has been previously detected. (C) 2003 Elsevier Ireland Ltd. All rights reserved.