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The forkhead-associated (FHA) domain is involved in protein-protein interaction by recognizing a phosphothreonine epitope on target proteins. In this study, we investigated in planta functions of the Arabidopsis FHA domain 2. AtFHA2 was mainly localized in the nucleus. Arabidopsis fha2 null mutants grew normally during the vegetative stage, but had severely reduced fertility during reproductive stage. The reduced fertility was mainly caused by defective stamen filament elongation, while female flower parts of the mutants were fertile. Additionally, the mutants had fewer stamens than the wild type and the vegetative organs of the mutants, such as cotyledons and leaves, had increased ploidy. These results suggest that AtFHA2 may play a role in a signaling pathway for the control of plant organ development.

In this study, we investigated the cellular functions of nuclear localizing protein (NLP) in Nicotiana benthamiana. The GFP fusion protein of Arabidopsis NLP is mostly targeted to the nucleus and cytosol, but it infrequently targets only the nucleus. Silencing of NLP using virus-induced gene silencing caused growth retardation and abnormal leaf development in N. benthamiana. At the cellular level, downregulation of NLP expression increased the size of pavement cells and stomata in the leaf tissues. NLP suppression also increased endoreduplication in leaf cells, suggesting a role of NLP in the endocycle. NLP transcript levels in leaves were significantly increased in response to infection with the nonhost pathogens. NLP deficiency attenuated HR cell death against nonhost pathogens and in response to gene-for-gene interaction. These findings suggest that NLP plays a role in plant development and plant defense responses against pathogens.

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