Plant biology

Activating Cytokinin in the Meristem

Science's STKE  13 Feb 2007:
Vol. 2007, Issue 373, pp. tw49
DOI: 10.1126/stke.3732007tw49

Cytokinin is a plant hormone synthesized from adenine that is important in controlling plant development and in meristem signaling. The meristem is a source of cells that differentiate to produce various parts of the plant, including stems, flowers, leaves, and roots. Kurakawa et al. characterized the rice mutant called lonely guy (log), which they found in a screen for plants defective in shoot meristem maintenance. These plants show defects in reproductive organ formation that result from premature termination of organ differentiation. Analysis of meristem markers revealed that the meristem pool was not maintained in the log mutants. Cloning and genome analysis of rice and Arabidopsis indicated that LOG belongs to a large gene family (11 members in rice). Analysis of the mRNA expression of LOG indicated that the gene was expressed in a small region of the floral meristem that included the stem cells. LOG had phosphoribohydrolase activity that converted a cytokinin nucleotide precursor into active cytokinin in a one-step process. This was unexpected, because cytokinin production was proposed to require a two-step activation by a nucleotidase and a nucleosidase. Analysis of the phenotypes of the log mutants was consistent with a cytokinin-activating activity for LOG--alleles with weak activity had weak phenotypes, whereas those completely lacking activity had a strong phenotype. Furthermore, the decrease in expression of cytokinin-induced genes in the meristem of log mutants supported the hypothesis that LOG activity in the meristem increases cytokinin activity.

T. Kurakawa, N. Ueda, M. Maekawa, K. Kobayashi, M. Kojima, Y. Nagato, H. Sakakibara, J. Kyozuka, Direct control of shoot meristem activity by a cytokinin-activating enzyme. Nature 445, 652-655 (2007). [PubMed]