Patterns of cell division revealed by transcriptional regulation of genes during the cell cycle in plants.

Abstract

Transcripts from five cell cycle related genes accumulate in isolated cells dispersed throughout the actively dividing regions of plant meristems. We propose that this pattern reflects gene expression during particular phases of the cell division cycle. The high proportion of isolated cells suggests that synchrony between daughter cells is rapidly lost following mitosis. This is the first time that such a cell specific expression pattern has been described in a higher organism. Counterstaining with a DNA specific dye revealed that transcripts from three genes (two mitotic cyclins and a cdc2‐like gene) accumulate during part of interphase and early mitosis whereas transcripts from a histone H4 gene are preferentially detected only in interphase cells. Double labelling for cyclin and histone H4 transcripts confirms that these genes are expressed in different cells, and therefore at different phases of the cell cycle. The results suggest that transcriptional regulation of cell cycle related genes may be important in controlling cell division in plants, and that these genes are useful markers for identifying cells at specific phases of the cell cycle within plant meristems.

Two bZIP proteins from Antirrhinum flowers preferentially bind a hybrid C‐box/G‐box motif and help to define a new sub‐family of bZIP transcription factors

“…The in situ experiments showed that the two bZIP genes had different but overlapping patterns of expression in Antirrhinum flowers so, potentially, bZIP911 could function in some places as a homodimer (for example in the endothecium and most of the cells of the carpel) and in others bZIP910 and bZIP911 could potentially interact © Blackwell Science Ltd, The Plant Journal, (1998), 13, 489-505 as heterodimers (for example in the tapetum and vascular tissues of the ovaries). The expression pattern of bZIP911 was similar to the reported pattern of a gene encoding histone H4 in Antirrhinum (Forbert et al, 1994), in particular in the absence of expression in the older bract and sepal primordia and the relatively strong expression in the anthers. This gene encoding histone H4 is relatively highly expressed in the vascular tissue of floral apices, as is bZIP910.…”

“…Transcriptional activation probably requires interaction with other factors, one possibility being the proteins binding to the neighbouring octomer motif conserved in many histone promoters, another being heterodimerization with other members of the bZIP protein family and yet another being binding to co-activators to increase bZIP activation specificity (Claret et al, 1996). The pattern of bZIP910 and bZIP911 gene expression shows a reasonably good correlation to expression of the gene encoding histone H4 in Antirrhinum inflorescences (Forbert et al, 1994) although post-transcriptional regulation may further modify the amount of each transcription factor active in any one cell.…”

“…Up to 15 transgenic tobacco plants transformed with each construct under the control of the double CaMV 35S promoter were examined for the levels of the bZIP transcripts in leaves. Leaves from selected plants expressing high levels of each transgene were also examined for transcript levels of histone genes (H4) (Forbert et al, 1994) and members of the tobacco CAB gene family (Chatterjee et al, 1996) and the small subunit gene of Rubisco (RBCS), by probing RNA gel blots. Loading was quantified by probing with the rDNA from pea to identify ribosomal RNA and with a UBIQUITIN cDNA clone from Antirrhinum.…”

“…Three independent transformants expressing bZIP910 with its 5Ј leader (910L) and without its 5Ј leader (910S), three independent transformants expressing bZIP911 with its 5Ј leader (911L) and one expressing bZIP911 without its 5Ј leader (911S) were compared to plants expressing bZIP910 and bZIP911 in antisense orientation (AS910 and AS911, respectively) and the average of two control plants transformed with vector alone (C). RNA gel blots were probed with genes encoding histone H4 (from Antirrhinum majus; a gift from John Doonan, Forbert et al, 1994), CAB (from tobacco; Chatterjee et al, 1996) and ubiquitin (from Antirrhinum majus). Transcript levels were quantified by phosphor imager and values were corrected for small variations in loading by standardization to the ubiquitin values.…”

CINCINNATA Controls Both Cell Differentiation and Growth in Petal Lobes and Leaves of Antirrhinum

“…HIS4 is expressed only in the S phase of the cell cycle, and only a proportion of the cells give a strong signal in proliferating tissue. CYCD3B, a key regulator of the cell cycle in plants, is not restricted to one phase of the cell cycle and is expressed throughout proliferating tissue (Fobert et al, 1994;Riou-Khamlichi et al, 1999;Gaudin et al, 2000).…”