Mutants on stalk strength are essential materials for the studies on the formation of plant cell wall. In this study, a brittle stalk mutant of maize, designated as Bk-x, was screened from a Mutator inserted mutant library. At the germination and early seedling stage, the mutant plants were indistinguishable from the normal ones. However, all of the plant organs were brittle after the 5th-leaf stage and remained brittle throughout the rest of the growing period. Microstructure observation showed that the cell wall in vascular bundle sheath of Bk-x was thinner than that in normal plants. The leaf mechanical strength in Bk-x was 77.9% of that in normal plants growing at Xishuangbanna (BN), Yunnan province and that was 61.7% in Wuhan (WH), Hubei Province, China. The proportion of cellulose was 12.3% in Bk-x, which was significantly lower than that in normal plants (26.7%), while the soluble sugar content was 36.1% in Bk-x, which is significantly higher than that in normal plants (12.4%). Genetic analysis using two F2 populations and one F2:3 families demonstrated that the trait of brittle stalk is controlled by a single recessive gene.

Mutator transposable element (Mu) has been used as an effective tool to clone maize (Zea mays L.) genes. One opaque endosperm mutant (mio16) was identified in a pool of Mu inserted mutants. A modified method, termed the double selected amplification of insertion flanking fragments (DSAIFF), was employed to isolate the Mu flanking fragments (MFFs) of mio16. The target site duplications (TSDs) isolated from the Msp I and Mse I digested MFFs had a same 9-bp sequence and were confirmed to be the flanking sequence of one identically inserted gene. Co-segregation analysis suggested that the MFFs were associated with the mutant opaque endosperm, and mio16 was mapped in silico onto the physical position ranged from 229 965021 to 229 965409 bp of the maize chromosome 4.09 bin. The full-length cDNA of the wild-type gene was obtained by an RT-PCR primer-scanning technique, and Mio16 was found to putatively encode a homolog of the Arabidopsis MAP3K delta-1 protein kinase. RT-PCR result the mRNA expression of mio16 region anchored by primers Mu20 and af276 was not interrupted by Mu insertion. Further researches will be done to elucidate how the expression of mio16 is alternated by Mu insertion.