A HAP complex, which consists of three subunits, namely HAP2 (also called NF-YA or CBF-B), HAP3 (NF-YB/CBF-A) and HAP5 (NF-YC/CBF-C), binds to CCAAT sequences in a promoter to control the expression of target genes. We identified 10 HAP2 genes, 11 HAP3 genes and 7 HAP5 genes in the rice genome. All the three HAP family genes encode a protein with a conserved domain in each family and various non-conserved regions in both length and amino acid sequence. These genes showed various expression patterns depending on genes, and various combinations of overlapped expression of the HAP2, HAP3 and HAP5 genes were observed. Furthermore, protein interaction analyses showed interaction of OsHAP3A, a ubiquitously expressed HAP3 subunit of rice, with specific members of HAP5. These results indicate that the formation of specific complex with various HAP subunits combinations can be achieved by both tissue specific expression of three subunit genes and specific interaction of three subunit proteins. This may suggest that the HAP complexes may control various aspects of rice growth and development through tissue specific expression and complex formation of three subunit members.

The estimation of hybrid rice seed purity is done conventionally by the grow out test (GOT), which is based on the assessment of morphological and floral characteristics in plants grown to maturity. For seed companies, large amounts of capital are locked up in the form of hybrid seed stock while awaiting the results of the GOT. With the objective of replacing the GOT with DNA based assays, cytoplasmic male sterile (CMS), restorer, and hybrid lines have been screened by means of microsatellite and sequence tagged site (STS) polymorphisms. A simple procedure for detecting heterozygosity and purity has been standardized and uses 6‐d‐old rice (Oryza sativa L.) seedlings, which could be used for detection of off‐types in hybrid seed lots. The extent of heterozygosity within parental lines of rice hybrids was assessed and the results suggest that a single, appropriately chosen microsatellite marker should be sufficient for assessing hybrid seed purity.

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