Recombinant AtNF-YA, a subunit of theArabidopsis CCAAT-binding transcription factor, forms a protein-DNA complex with mammalian NF-YB and NF-YC

The evolutionary conserved CCAAT binding protein NF-Y is a common regulatory DNA binding protein consisting of three distinct subunits. Unlike yeast and mammals, in which only a single copy of each subunit is encoded,Arabidopsis encodes a multi-gene family for each subunit in its genome. Compared with the NF-Y of mammals or yeast, very little is known about plant NF-Y homologs. HereArabidopsis NF-YA subunits were isolated to determine whether they could form a hete-rotrimeric NF-Y complex with mammalian NF-YB and NF-YC. This resultant chimeric NF-Y complex had DNA binding ability to the same CCAAT sequences as those of the other life systems. Therefore, it is possible that plant NF-Y homologs might have biochemical characteristics similar to mammalian NF-Y, thereby suggesting its functional conservation among organisms.     

Comparative analysis of rice MADS-box genes expressed during flower development

MADS-box genes involved in flower development have been isolated and studied in a wide variety of plant species. However, most of these studies are related to dicot species like Antirrhinum majus, Arabidopsis thaliana and Petunia hybrida. Although the floral structures of typical monocot and dicot flowers differ substantially, previous studies indicate that MADS-box genes controlling floral organ identity in dicots can also be identified in monocot plants like rice and maize. To extend this study further to obtain a more global picture of monocot and dicot MADS-box gene evolution, we performed a phylogenetic study using MADS-box genes from A. thaliana and Oryza sativa. Furthermore, we investigated whether the identified orthologues of Arabidopsis and rice have a conserved expression profile that could indicate conservation of function.     

Asymmetric evolution of duplicate genes encoding the CCAAT-binding factor NF-Y in plant genomes

NF-Y is a ubiquitous CCAAT-binding factor composed of NF-YA, NF-YB and NF-YC. Multiple genes encoding NF-Y subunits have been identified in plant genomes. It remains unclear whether the duplicate genes underwent different evolutionary patterns. Likelihood-ratio tests were used to examine whether the amino acid substitution rates are the same between duplicate genes. The influences of selection on evolution were evaluated by comparing the conservative and radical amino acid substitution rates, as well as maximum-likelihood analysis. Some NF-YB and NF-YC duplicates showed significant evidence of asymmetric evolution but not the NF-YA duplicates. Most amino acid replacements in the NF-YB and NF-YC duplicates result in changes in hydropathy, polar requirement and polarity. The physicochemical changes in the sequences of NF-YB seem to be coupled to asymmetric divergence in gene function. Plant NF-Y genes have evolved in different patterns. Relaxed selective constraints following gene duplication are most likely responsible for the unequal evolutionary rates and distinct divergence patterns of duplicate NF-Y genes. Positive selection may have promoted amino acid hydropathy changes in the NF-YC duplicates.     

Wound signaling-coordination of the octadecanoid and MAPK pathways

Plants have developed integrated signaling networks that play a pivotal role in mediating the perception of and response to environmental factors, including wounding, a common stress. Wound signaling is known to involve at least two major signaling pathways—the octadecanoid and the MAPK pathways. These two pathways have been investigated in model dicotyledoneous (dicot) and monocotyledoneous (monocot) plant species such as alfalfa, Arabidopsis, tobacco, tomato, barley, maize and rice. Our careful analysis of available findings, to date, on wound signaling point towards a remarkable difference in coordination between the octadecanoid and the MAPK pathways in dicots and rice (Oryza sativa L.), a monocot cereal crop model plant. In this review we discuss the current understanding on these two critical pathways and propose a view on their relationship in rice with respect to wound signaling in dicot plants.     

Identification,characterization and interaction of <Emphasis Type="Italic">HAP</Emphasis> family genes in rice

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. Nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB288027 to AB288048 and BR000373 to BR000375.     

植物HAP3转录因子研究进展

HAP(NF-Y或CBF)是一类重要的转录因子,可以与CCAAT框结合并控制基因的表达,广泛分布于酵母、哺乳动物及植物细胞中.在哺乳动物和植物细胞中,HAP复合体包括3个不同的亚基:HAP2/NF-YA/CBF-B、HAP3/NF-YB/CBF-A及HAP5/NF-YC/CBF-C.HAP3转录因子在植物胚胎发育、叶绿素生物合成、花期调控等方面有重要作用.介绍植物HAP3转录因子结构特点、生物学功能等方面的最新研究进展.     

Dissection of the NF-Y transcriptional activation potential.

NF-Y is a trimeric CCAAT-binding factor with histone fold subunits (NF-YB/NF-YC) and bipartite activation domains located on NF-YA and NF-YC. We reconstituted the NF-Y activation potential in vivo with GAL4 DBD fusions. In the GAL4-YA configuration, activation requires co-expression of the three subunits; with GAL4-YB and GAL4-YC, transfections of the histone fold partners are sufficient, provided that the Q-rich domain of NF-YC is present. Combinations of mutants indicate that the Q-rich domains of NF-YA and NF-YC are redundant in the trimeric complex. Glutamines 101 and 102 of NF-YA are required for activity. We assayed NF-Y on different promoter targets, containing single or multiple GAL4 sites: whereas on a single site NF-Y is nearly as powerful as VP16, on multiple sites neither synergistic nor additive effects are observed. NF-Y activates TATA and Inr core elements and the overall potency is in the same range as other Q-rich and Pro-rich activation domains. These results represent the first in vivo evidence of subunit interactions studies and further support the hypothesis that NF-Y is a general promoter organizer rather than a brute activator.