Modification of nitrogen remobilisation, grain fill and leaf senescence in maize (Zea mays L.) by transposon insertional mutagenensis in a protease gene

A maize (Zea mays) senescence-associated legumain gene, See2β, was characterized at the physiological and molecular levels to determine its role in senescence and resource allocation.
• A reverse-genetics screen of a maize Mutator (Mu) population identified a Mu insertion in See2β. Maize plants homozygous for the insertion were produced. These See2 mutant and sibling wild-type plants were grown under high or low quantities of nitrogen (N).
• The early development of both genotypes was similar; however, tassel tip and collar emergence occurred earlier in the mutant. Senescence of the mutant leaves followed a similar pattern to that of wild-type leaves, but at later sampling points mutant plants contained more chlorophyll than wild-type plants and showed a small extension in photosynthetic activity. Total plant weight was higher in the wild-type than in the mutant, and there was a genotype × N interaction. Mutant plants under low N maintained cob weight, in contrast to wild-type plants under the same treatment.
• It is concluded, on the basis of transposon mutagenesis, that See2β has an important role in N-use and resource allocation under N-limited conditions, and a minor but significant function in the later stages of senescence.