Practice question

MCQ

Question

MONOPTEROS (MP) mutation results in:

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Choose one · Correct answer highlighted

Root and hypocotyl absence Correct Cotyledon absence Leaf absence Floral organ absence

Explanation

MONOPTEROS encodes ARF5 auxin response factor activated when high auxin promotes TIR1/AFB-mediated ubiquitination and degradation of BODENLOS/IAA12 repressor in nucleus. Liberated MP directly induces transcription of PIN1, TMO5, ATHB8, and other vascular precursor genes in basal embryo and provascular strands. In monopteros null mutants hypophysis specification fails, basal lineage divides irregularly, seedlings germinate lacking embryonic root and hypocotyl while retaining cotyledons and functional shoot meristem. This reveals essential role of ARF-mediated transcriptional activation downstream of auxin perception for establishing lower embryonic tier and root stem cell niche.

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