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1.  Timing Is Everything: Highly Specific and Transient Expression of a MAP Kinase Determines Auxin-Induced Leaf Venation Patterns in Arabidopsis  
Molecular Plant  2014;7(11):1637-1652.
The Arabidopsis MAP kinase AtMPK10 has long been considered as a pseudo-gene without visible function for the plant. Here we show that AtMPK10 is functional only in a very narrow time window in leaves at sites of local auxin maxima where it regulates leaf venation complexity together with the upstream kinase AtMKK2.
Mitogen-activated protein kinase (MAPK) cascades are universal signal transduction modules present in all eukaryotes. In plants, MAPK cascades were shown to regulate cell division, developmental processes, stress responses, and hormone pathways. The subgroup A of Arabidopsis MAPKs consists of AtMPK3, AtMPK6, and AtMPK10. AtMPK3 and AtMPK6 are activated by their upstream MAP kinase kinases (MKKs) AtMKK4 and AtMKK5 in response to biotic and abiotic stress. In addition, they were identified as key regulators of stomatal development and patterning. AtMPK10 has long been considered as a pseudo-gene, derived from a gene duplication of AtMPK6. Here we show that AtMPK10 is expressed highly but very transiently in seedlings and at sites of local auxin maxima leaves. MPK10 encodes a functional kinase and interacts with the upstream MAP kinase kinase (MAPKK) AtMKK2. mpk10 mutants are delayed in flowering in long-day conditions and in continuous light. Moreover, cotyledons of mpk10 and mkk2 mutants have reduced vein complexity, which can be reversed by inhibiting polar auxin transport (PAT). Auxin does not affect AtMPK10 expression while treatment with the PAT inhibitor HFCA extends the expression in leaves and reverses the mpk10 mutant phenotype. These results suggest that the AtMKK2–AtMPK10 MAPK module regulates venation complexity by altering PAT efficiency.
PMCID: PMC4228985  PMID: 25064848
Arabidopsis MAP kinase; leaf development; polar auxin transport; leaf venation pattern.
2.  Trehalose-6-Phosphate: Connecting Plant Metabolism and Development 
Beyond their metabolic roles, sugars can also act as messengers in signal transduction. Trehalose, a sugar found in many species of plants and animals, is a non-reducing disaccharide composed of two glucose moieties. Its synthesis in plants is a two-step process, involving the production of trehalose-6-phosphate (T6P) catalyzed by trehalose-6-phosphate synthase (TPS) and its consecutive dephosphorylation to trehalose, catalyzed by trehalose-6-phosphate phosphatase (TPP). T6P has recently emerged as an important signaling metabolite, regulating carbon assimilation and sugar status in plants. In addition, T6P has also been demonstrated to play an essential role in plant development. This review recapitulates the recent advances we have made in understanding the role of T6P in coordinating diverse metabolic and developmental processes.
PMCID: PMC3355582  PMID: 22639606
trehalose; trehalose-6-phosphate; TPS; TPP; development
3.  The FANTASTIC FOUR proteins influence shoot meristem size in Arabidopsis thaliana 
BMC Plant Biology  2010;10:285.
Throughout their lives plants produce new organs from groups of pluripotent cells called meristems, located at the tips of the shoot and the root. The size of the shoot meristem is tightly controlled by a feedback loop, which involves the homeodomain transcription factor WUSCHEL (WUS) and the CLAVATA (CLV) proteins. This regulatory circuit is further fine-tuned by morphogenic signals such as hormones and sugars.
Here we show that a family of four plant-specific proteins, encoded by the FANTASTIC FOUR (FAF) genes, has the potential to regulate shoot meristem size in Arabidopsis thaliana. FAF2 and FAF4 are expressed in the centre of the shoot meristem, overlapping with the site of WUS expression. Consistent with a regulatory interaction between the FAF gene family and WUS, our experiments indicate that the FAFs can repress WUS, which ultimately leads to an arrest of meristem activity in FAF overexpressing lines. The finding that meristematic expression of FAF2 and FAF4 is under negative control by CLV3 further supports the hypothesis that the FAFs are modulators of the genetic circuit that regulates the meristem.
This study reports the initial characterization of the Arabidopsis thaliana FAF gene family. Our data indicate that the FAF genes form a plant specific gene family, the members of which have the potential to regulate the size of the shoot meristem by modulating the CLV3-WUS feedback loop.
PMCID: PMC3023791  PMID: 21176196

Results 1-3 (3)