CHARACTERIZATION AND EXPRESSION OF RPOC2 IN CMS AND FERTILE LINES OF SORGHUM

A 165 bp deletion in the middle of rpoC2, the plastid gene which encod es the RNA polymerase beta '' subunit, was identified in the small-ant hered types of CMS sorghum, Sorghum bicolor (L.). Moench, containing A l, A2, A5, and A6 cytoplasms. It was previously shown that the amino a cid sequence deleted in these CMS lines is in a monocot-specific regio n that contains several protein motifs that are characteristic of seve ral transcription factors. Using primers flanking the deletion in PCR analyses, various types of CMS lines, some of which are used in hybrid sorghum production, were classified into two groups. CMS lines contai ning Al, A2, A5, A6 cytoplasms display the deletion in rpoC2. These li nes have small anthers in which pollen development is arrested at an e arly stage and in which usually only empty exines are found. CMS lines containing A3, A4, and 9E cytoplasms do not possess the deletion. The se lines have large anthers in which pollen degenerates at a later sta ge. Run-on transcription assays using 15 chloroplast genes showed that chloroplast gene transcription rates are similar in CMS and fertile ( maintainer and restorer) lines and F-1 in seedling leaves. Analyses of RNA blots indicated that rbcL, rpoB and rpoC2 transcripts are accumul ated mainly in the leaves and low in the inflorescence tissues and pol len. These data document plastid gene expression in leaves and non-pho tosynthetic tissues from CMS and fertile fines of sorghum.