The plant cell cycle − 15 years on

Summary The basic components of the plant cell cycle are G1 (postmitotic interphase), S‐phase (DNA synthesis phase), G2 (premitotic interphase) and mitosis/cytokinesis. Proliferating cells are phosphoregulated by cyclin‐dependent protein kinases (CDKs). Plant D‐type cyclins are sensors of the G0 to G1 transition, and are also important for G2/M. At G1/S, the S‐phase transcription factor, ‘E2F’, is released from inhibitory retinoblastoma protein. Negative regulation of G1 events is through KRPs (Kip‐related proteins). Plant S‐phase genes are similar to animal ones, but timing of expression can be different (e.g. CDC6 at the start of S‐phase) and functional evidence is limited. At G2/M, A‐type and the unique B‐type CDKs when bound to A, B and D cyclins, drive cells into division; they are negatively regulated by ICK1/2 and perhaps also by WEE1 kinase. In Arabidopsis , a putative CDC25 lacks a regulatory domain. Mitosis depends on correct temporal activity of CDKs, Aurora kinases and anaphase promotion complex; CDK‐cyclin B activity beyond metaphase is catastrophic. Endoreduplication (re‐replication of DNA in the absence of mitosis) is characterized by E2F expression and down‐regulation of mitotic cyclins. Some cell size data support, whilst others negate, the idea of cell size having an impact on development. Contents Summary 261 I. Introduction 262 II. Plant CDKs and cyclins 263 III. G0 → G1 → S – the dawn awakening 263 IV. S‐phase – life gets replicated 264 V. G2/M – let's dance 266 VI. Mitosis – strictly come dancing 268 VII. Cytokinesis – partitioning life 269 VIII. M/G1 – party over 270 IX. Endocycles – a curious life of their own 270 X. Cell size 270 XI. Root branching 271 XII. Conclusions 271 Acknowledgements 273 References 273