MCI BFU2011-22825, 2012-2014

Principal Investigator: José Luis Micol.
Investigators: David Esteve Bruna, Rubén Casanova Sáez, David Wilson Sánchez, Amani Toumi, Sara Jover Gil, Eduardo Mateo Bonmatí and Tamara Muñoz Nortes.
Instituto de Bioingeniería. Universidad Miguel Hernández.

A large-scale analysis of the morphogenetic role of translation and compensation in Arabidopsis leaf growth and development

Plant leaves are the best solar panels ever built, and they also perform well as air purifiers and food factories. Leaves efficiently trap sunlight, remove carbon dioxide from the air, and are the ultimate source of most of the oxygen that we breathe and of the food that we eat. Understanding how a leaf is made is important for several reasons, which include gaining knowledge of the biology and evolution of a multicellular organ with no equivalents in the animal kingdom, as well as identifying  —and eventually manipulating, to increase crop yield— the genetic, environmental, and hormonal cues that determine its final architecture and function.

To shed light on the making of plant leaves, in 1993 we initiated an attempt to saturate the genome of the model organism Arabidopsis thaliana with viable mutations that cause abnormal leaf morphology. The identified mutations fell into 147 complementation groups. Using a high-throughput gene mapping method that we developed, we have already cloned 47 of these genes identified by mutation. The products of these genes participate in various developmental processes, such as polar cell expansion, transduction of hormonal signals, gene regulation, plastid biogenesis, and chromatin remodeling, among others. The broad spectrum of leaf morphological alterations that we identified is helping to dissect specific leaf developmental processes.

The objective of this project is to further our understanding of two intriguing phenomena that recently reentered the leaf scenario. One is the unexpected relationship between translation and leaf dorsoventrality, recently confirmed by the severe abaxialization of double mutants involving loss-of-function alleles of the developmental selector genes AS1 and AS2 and some genes encoding ribosomal proteins. The second unexplained phenomenon is the compensatory cell enlargement experienced by some leaf mutants, in which a reduction in cell number is compensated by their increased cell size compared with the wild type. This compensation suggests that cell cycling and cell expansion are integrated in leaf primordia via cell-to-cell communication.

We will combine traditional linkage analysis and next-generation sequencing techniques in order to positionally clone 40 non-allelic mutations already isolated in the laboratory of J.L. Micol, which affect leaf morphology, in most cases causing small, pointed and dentate vegetative leaves. We will accomplish the phenotypic and genetic characterization of these mutants —which will include genetic interaction analyses and morphometry— in order to determine the number, size and shape of mesophyll and pavement epidermal cells. We will also confirm their molecular identity, visualize their expression patterns and perform promotor swapping studies.