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Scientists Propose a Two-step Regulation of Leaf Axil Meristematic Cell Population
Shoot branching is a key factor affecting plant architecture and crop yield. Axillary meristems established in the leaf axils enable shoot branching.
Previous work from Dr. JIAO Yuling’s group at the State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, showed the involvement of phytohormones in the regulation of axillary meristem initiation (Wang et al., 2014; Han et al., 2014), and have preliminary resolved the gene regulatory network underlying axillary meristem initiation (Tian et al., 2014).  
In a recent study, researchers from Dr. JIAO’s group found that a meristematic cell population acting as ancestor cells for axillary meristem initiation. This leaf axil meristematic cell lineage continuously expresses SHOOT MERISTEMLESS (STM) (Green in the Figure below). Through genetic analysis and laser ablation, the scientists showed that this auxin minimum-dependent meristematic cell population was required for axillary meristem initiation. In more mature leaves, REVOLUTA (REV), a member of HD-Zip III transcription factor family, directly up-regulates STM expression in the leaf axil meristematic cells. Different epigenetic modifications of the STM genomic region contribute to the cell-type specific binding of REV.
Taken together, they proposed a threshold model for axillary meristem initiation. Initially, a low level of STM expression is maintained, which depends on the leaf axil auxin minimum, to retain meristematic competence. Later, the maintained STM expression is up-regulated by REV to promote axillary meristem initiation (see Figure below).
This work, entitled “Two-step Regulation of a Meristematic Cell Population Acting in Shoot Branching in Arabidopsis”, has been published on PLoS Genetics (10.1371/journal.pgen.1006168) with PhD candidate SHI Bihai and Assistant Research Scientist Dr. ZHANG Cui as co-first authors. This research was supported by the National Basic Research Program of China (973 Program), National Natural Science Foundation of China, and the State Key Laboratory of Plant Genomics.
Conceptual model showing two-step regulation during axillary meristem initiation. (Image by IGDB)
Dr. JIAO Yuling