miRNA Accumulation Correlates with Increased Phloem Cell Proliferation in Tomato hawaiian skirt Mutants

Fabien Lombardo^1*Tarek El mestari²Thomas Kirat²Muhammad Ijaaz Jondah²Julie Marsaudon²Norbert Bollier³Chiaki Matsukura¹

• ¹Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
• ²Universite de Bordeaux College Sciences et Technologies, Talence, France
• ³Université de Bordeaux, INRAE, UMR1332 Biologie du Fruit et Pathologie, Villenave d’Ornon, France

The cambium is the meristem responsible for production of plant vascular tissues, the xylem (wood) and phloem, during plant radial growth. Due to its internal location and relatively low cell number, the biology of the cambium remains less well understood com-pared to other plant meristems. The tomato hws mutant exhibits miRNA accumulation and produces a markedly enlarged phloem, suggesting a role for miRNAs in regulating vascular development. This study aims to identify the accumulated miRNAs associated with the vascular phenotype in hws mutants and characterize their impact on phloem development kinetics. To achieve this, we analyzed the vascular phenotype of hws mutants using pedicel and stem sections examined using light and scanning electron microscopy, alongside RNA sequencing of miRNAs from pedicels. Our findings reveal increased cell division rates during the phloem expansion phase in hws-1 while xylem is reduced due to a shortened expansion phase in pedicels. Key miRNAs, including miR319 and miR164, were identified as highly accumulated in the mutant pedicels. Vascular phenotypes in stems were consistent with those observed in pedicels. Our findings underscore the potential for manipulating miRNA levels to improve phloem capacity and possibly crop yields through targeted genetic strategies.