Abstract
DnaJ proteins are essential co-chaperones involved in abiotic and biotic stress responses. Arabidopsis AtDjA3 gene encodes a molecular co-chaperone of 420 amino acids, which belongs to the J-protein family. In this study, we report the functional characterization of the AtDjA3 gene using the Arabidopsis knockout line designated j3 and the 35S::AtDjA3 overexpression lines. Loss of AtDjA3 function was associated with small seed production. In fact, j3 mutant seeds showed a reduction of 24% in seed weight compared to Col-0 seeds. Expression analysis showed that the AtDjA3 gene was modulated in response to NaCl, glucose, and abscisic acid (ABA). The j3 line had increased sensitivity to NaCl and glucose treatments in the germination and cotyledon development in comparison to parental Col-0. Furthermore, the j3 mutant line exhibited higher ABA sensitivity in comparison to parental Col-0 and 35S::AtDjA3 overexpression lines. In addition, we examined the expression of ABI3 gene, which is a central regulator in ABA signaling, in j3 mutant and 35S::AtDjA3 overexpression lines. Under 5 μM ABA treatment at 24 h, j3 mutant seedlings displayed higher ABI3 expression, whereas in 35S::AtDjA3 overexpression lines, ABI3 gene expression was repressed. Taken together, these results demonstrate that the AtDjA3 gene is involved in seed development and abiotic stress tolerance.
Highlights
Seed germination and seedling establishment are the most critical stages of survival during the life cycle of an individual plant (Daszkowska-Golec, 2011)
In order to evaluate the seed width and length, and testa morphology of the Atdja3-null mutant line and 35S::AtDjA3 overexpression lines, micrographs of seeds were taken by environmental scanning electron microscopy (eSEM) (Figures 1B–D, respectively)
One of the major molecular mechanisms to re-establish cellular homeostasis and protect cellular components under abiotic stress is the expression of stress response genes, which encode molecular chaperones such as Heat Shock Proteins (HSP)
Summary
Seed germination and seedling establishment are the most critical stages of survival during the life cycle of an individual plant (Daszkowska-Golec, 2011). Seeds are exposed to a wide range of unfavorable environmental conditions that induce stress, and have a negative impact on germination, growth, and development (Rao et al, 2006). Seeds have developed defense mechanisms that allow them to tolerate and respond rapidly to unfavorable conditions (Koornneef et al, 2002; Vallejo et al, 2010). Heat Shock Proteins (HSP) are accumulated during abiotic stress as a defense mechanism, and at the later stages of seed development appear to play a protective role in desiccation tolerance. AtDjA3 and Plant Stress (Wehmeyer and Vierling, 2000; Koornneef et al, 2002). HSPs are classified into five classes according to their molecular weight: HSP100, HSP90, HSP70, HSP60, and small HSP (sHSP; Wang et al, 2004)
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