MiR156targeted Squamosa Promoter-binding proteins (SPLs) regulate fruit development and determinacy

Author(s)

Geraldo Felipe Ferreira e Silva

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2012-04-11

Examining board members

Fabio Tebaldi Silveira Nogueira; Maria Helena de Souza Goldman; Daniel Scherer de Moura

• Advisor: Fabio Tebaldi Silveira Nogueira

Abstract

Many plants have indeterminate growth and are capable of producing new organs and tissues throughout their life. This capability is partially due to the highly regulated expression of specific genes such as SQUAMOSA Promoter-Binding Protein-Like (SPL) genes. SPLs encode plant-specific transcription factors that play important roles in development, such as phase transition, plant architecture, and fruit ripening. Most SPL genes are post-transcriptionally regulated by the microRNA (miRNA) miR156. Although some developmental aspects regulated by SPLs have been well studied, their molecular roles during fruit development are poorly understood. In this work, we generated 22 transgenic events of Solanum lycopersicum cv. Micro-Tom (MT) overexpressing AtMIR156b precursor. Transgenic plants exhibit abnormal leaf and flower morphology and altered vegetative architecture. Interestingly, most events display navel-like fruits that are seedless and characterized by the growth of secondary fruits and present leaf-like structures as well as ectopic flowering meristems. By using RT-qPCR, we found a robust correlation between miR156/SPL expression and the fruit phenotype, suggesting that this pathway regulates tomato fruit development and determinacy. The tomato mutant Mouse ears (Me) displays a weak level of fruit indeterminacy. Levels of mature miR156 transcripts are higher in fruits from the mutant as comparing to MT fruits, but significantly lower than in transgenic fruits. Eight tomato SPLs were downregulated at variable levels in fruits from distinct transgenic events and Me plants. The MADS-type of transcription factor Macrocalyx (MC) gene is an orthologue of Arabidopsis AP1 (a direct in vivo target of SPL3) and affects tomato inflorescence determinacy and sepal development. MC was severely downregulated in fruits from transgenics but not in fruits from Me mutant. This data suggests that the MC misregulation may lead to the strong fruit indeterminacy phenotype observed in the transgenic events. Taken together, our data suggest a new function for miR156/SPL pathway in regulating fruit development and determinacy likely through the regulation of MC expression. (AU)

• FAPESP's process: 09/12710-7 - The role of metabolic pathways regulated by the microRNA156 in bud outgrowth
• Grantee: Geraldo Felipe Ferreira e Silva
• Support Opportunities: Scholarships in Brazil - Master