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11 Mar 2016

News: CRAG researchers discover that plant mesophyll is crucial for epidermal trichome formation

The new paper, published in Plant Physiology, challenges the present theories on epidermal trichome formation and point to TEMPRANILLO genes expressed in the mesophyll as key regulators for this process


Trichomes are epidermal “hairs” or elongations present on the surfaces of the leaves and other aerial organs of most plants. Trichomes defend plants against insect herbivores, virus, UV light, and excessive water loss. In some plants, trichomes can also synthetize and store specialized metabolites with commercial value. As an example, the trichomes of the Artemisia annua produce the compound artemisinin, a molecule with antimalarial effect whose discoverer, Prof. Youyou Tu, received the Nobel Prize in Medicine in 2015.

The current models on trichome formation state that trichome proliferation and development involve various genetic regulatory pathways active in the epidermis, including those activated by the hormones Gibberellins (GA) and cytokinins (CK). A team led by the CRAG-CSIC researcher Soraya Pelaz, have now discovered that TEMPRANILLO (TEM) genes expressed in the mesophyll cells are crucial for the epidermal trichome formation, suggesting a previously unknown non-cell-autonomous regulation mechanism.

Using the model plant Arabidopsis thaliana, CRAG researchers increased and decreased the expression of TEM genes specifically in the mesophyll of the rosette leaves and found that the plant responded to this change by decreasing and increasing the number of trichomes, respectively.  Since TEM transcription factors are known to repress the synthesis of the GA hormone during floral induction, the researchers sought to unveil if this mechanism was also involved in trichome formation. The GA hormone quantifications in TEM mutants demonstrated that these transcription factors effectively regulate both GA biosynthesis and trichome initiation.  Afterwards, the team applied an exogenous fluorescent-GA to study the hormone spatial distribution and accumulation “We were surprised to find that fluorescently labeled GA3 accumulated exclusively in the mesophyll of the leaves but not in the epidermis, suggesting a cell to cell active transport of the GA”, explains Luis Matías-Hernández, first author of the study. Further experiments showed that GA distribution is controlled by TEM transcription factors through the modulation of specific GA transporters (NPF).

“This work provides significant findings as it unravels communication from a cell layer (the mesophyll) that results in cell differentiation processes of another layer (epidermal trichomes). In addition, this work is important as it pinpoints the mesophyll as a new target for biotechnological strategies since trichomes store metabolites with value as pharmaceuticals for cancer and malaria treatments, for example”, says the senior author, Soraya Pelaz.  

Other authors of the study, which has recently been published in Plant Physiology, are Andrea E. Aguilar-Jaramillo, Michela Osnato and Paula Suárez-López, from CRAG (Spain), and Roy Weinstain and Eilon Shani from the Tel Aviv University (Israel).


For more information:

Plant Physiology March 2016 vol. 170 no. 3 1624-1639 TEMPRANILLO reveals the mesophyll as crucial for epidermal trichome formation. Matias-Hernandez L, Aguilar-Jaramillo AE, Osnato M, Weinstain R, Shani E, Suárez-López P, Pelaz S

Comment: Plant Physiology March 2016 vol. 170 no. 3 1174-1175 Trichome Formation: Gibberellins on the Move. Yuling Jiao.

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