An OsWRKY11 gene, which encodes a transcription factor with the WRKY domain, was identified as one of the genes that was induced by both heat shock and drought stresses in seedlings of rice (Oryza sativa L.). To determine if overexpression of OsWRKY11 confers heat and drought tolerance, OsWRKY11 cDNA was fused to the promoter of HSP101 of rice and introduced into a rice cultivar Sasanishiki. Overexpression of OsWRKY11 was induced by heat treatment. After heat pretreatment, the transgenic lines showed significant heat and drought tolerance, as indicated by the slower leaf-wilting and less-impaired survival rate of green parts of plants. They also showed significant desiccation tolerance, as indicated by the slower water loss in detached leaves. Our results indicate that the OsWRKY11 gene plays a role in heat and drought stress response and tolerance, and might be useful for improvement of stress tolerance.

Self-maintenance of the shoot apical meristem (SAM), from which aerial organs are formed throughout the life cycle, is crucial in plant development. Class I Knotted1-like homeobox (KNOX) genes restrict cell differentiation and play an indispensable role in maintaining the SAM. However, the mechanism that positively regulates their expression is unknown. Here, we show that expression of a rice (Oryza sativa) KNOX gene, Oryza sativa homeobox1 (OSH1), is positively regulated by direct autoregulation. Interestingly, loss-of-function mutants of OSH1 lose the SAM just after germination but can be rescued to grow until reproductive development when they are regenerated from callus. Double mutants of osh1 and d6, a loss-of-function mutant of OSH15, fail to establish the SAM both in embryogenesis and regeneration. Expression analyses in these mutants reveal that KNOX gene expression is positively regulated by the phytohormone cytokinin and by KNOX genes themselves. We demonstrate that OSH1 directly binds to five KNOX loci, including OSH1 and OSH15, through evolutionarily conserved cis-elements and that the positive autoregulation of OSH1 is indispensable for its own expression and SAM maintenance. Thus, the maintenance of the indeterminate state mediated by positive autoregulation of a KNOX gene is an indispensable mechanism of self-maintenance of the SAM.

During postembryonic development of higher plants, the shoot apical meristem produces lateral organs in a regular spacing (phyllotaxy) and a regular timing (plastochron). Molecular analysis of mutants associated with phyllotaxy and plastochron would greatly increase understanding of the developmental mechanism of plant architecture because phyllotaxy and plastochron are fundamental regulators of plant architecture. pla1 of rice is not only a plastochron mutant showing rapid leaf initiation without affecting phyllotaxy, but also a heterochronic mutant showing ectopic shoot formation in the reproductive phase. Thus, pla1 provides a tool for analyzing the molecular basis of temporal regulation in leaf development. In this work, we isolated the PLA1 gene by map-based cloning. The identified PLA1 gene encodes a cytochrome P450, CYP78A11, which potentially catalyzes substances controlling plant development. PLA1 is expressed in developing leaf primordia, bracts of the panicle, and elongating internodes, but not in the shoot apical meristem. The expression pattern and mutant phenotype suggest that the PLA1 gene acting in developing leaf primordia affects the timing of successive leaf initiation and the termination of vegetative growth.

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.