Gene expression signatures during leaf development

Martinez et al. use laser capture microdissection and transcriptomic sequencing to explore how gene expression patterns regulate early morphogenesis of the compound tomato leaf.

 By Ciera Martinez, University of California, Berkeley

Neelima Sinha, University of California, Davis

 Background: Leaf development involves cell division, expansion, and cellular specialization in specific positions along the middle to margin and top to bottom axes of a leaf. These regions expand and develop at different rates.

Question:  We wanted to understand what the differences in development are between the middle and the margin of a leaf. We used a microscope-based method and small lasers to dissect out six tiny regions of a young tomato leaf.

Findings:  Using precisely dissected regions of the young leaf, we generated a global gene expression atlas of the early developing tomato leaf. We describe when and where leaf cells first begin photosynthesis. Surprisingly, photosynthetic capability is first seen in the middle regions of the leaf and not the blade. We also describe the role of the plant hormone auxin in various regions of the leaf.  We evaluated the role of gene expression in each domain in conferring the ability to continue cell division and permitting blade outgrowth. Knockout mutants of one gene, BLADE-ON-PETIOLE2, exhibited shoot apical meristem formation on leaves, highlighting the role of this gene in regulating the balance between cell division and blade outgrowth.

Next steps: Since our gene expression dataset is extremely large, we will test more genes that were identified from the dataset to see the exact way in which they control leaf shape early in development.

 Ciera C. Martinez, Siyu Li, Margaret R. Woodhouse, Keiko Sugimoto, and Neelima R. Sinha (2021). Spatial transcriptional signatures define margin morphogenesis along the proximal-distal and medio-lateral axes in tomato (Solanum lycopersicum) leaves. Plant Cell