TheArabidopsisD-Type Cyclin CYCD4 Controls Cell Division in the Stomatal Lineage of the Hypocotyl Epidermis

Abstract

Cyclin D (CYCD) plays an important role in cell cycle progression and reentry in response to external signals. Here, we demonstrate that Arabidopsis thaliana CYCD4 is associated with specific cell divisions in the hypocotyl. We observed that cycd4 T-DNA insertion mutants had a reduced number of nonprotruding cells and stomata in the hypocotyl epidermis. Conversely, CYCD4 overexpression enhanced cell division in nonprotruding cell files in the upper region of the hypocotyls, where stomata are usually formed in wild-type plants. The overproliferative cells were of stomatal lineage, which is marked by the expression of the TOO MANY MOUTHS gene, but unlike the meristemoids, most of them were not triangular. Although the phytohormone gibberellin promoted stomatal differentiation in the hypocotyl, inhibition of gibberellin biosynthesis did not prevent CYCD4 from inducing cell division. These results suggested that CYCD4 has a specialized function in the proliferation of stomatal lineage progenitors rather than in stomatal differentiation. We propose that CYCD4 controls cell division in the initial step of stomata formation in the hypocotyl.

A high-throughput bimolecular fluorescence complementation protein-protein interaction screen identifies functionalArabidopsisCDKA/B-CYCD4/5 complexes

“…3F). In agreement with previous reports, the ploidy level of the CYCD4;2OE line was not affected 19 (data not shown).…”

“…19 In contrast, in our experiments, in plants overexpressing either the CYCD4;2 or the CDKA;1-CYCD4;2 complex, the cotyledons were 35% and 58% larger than those of the wild type and the CDKA;1OE line, respectively (Fig. 3A).…”

“…D4-type cyclins have previously been proposed to function as positive regulators of cell division in different tissues of Arabidopsis and to form active kinase complexes with CDKA;1. 19,24 However, binding of CYCD4 to CDKB2;1 proteins meristematic cells is established (Fig. 2E and F).…”

“…Because CYCD4;1 and CYCD4;2 control cell division in the stomatal lineage in hypocotyls, 19 we analyzed the hypocotyls of the CDKA;1-CYCD4;2OE line and found, consistently, that the number of stomata had increased by 55% in seven-day-old seedlings overexpressing CYCD4;2 and by 150% in the seedlings of the CDKA;1-CYCD4;2OE line (Fig. 4A).…”

“…Because the two D4-type cyclins function redundantly in Arabidopsis 19 and no differences between CDKB1;1 and CDKA;1 complexes had been observed, only the CDKA;1-CYCD4;2 transgenic lines are described. Based on the fluorescence signal, the CDKA;1-CYCD4;2 complex was detected in most plant tissues.…”