DlRan3A is involved in hormone, light, and abiotic stress responses in embryogenic callus of Dimocarpus longan Lour.

Abstract

Ras-related nuclear protein (Ran) GTPase plays an important role in nucleo-cytoplasmic transportation of proteins and RNA, mitotic spindle assembly, microtubule assembly and nuclear envelope (NE) assembly. We previously identified the full-length cDNAs and a DNA of DlRan3A from longan (Dimocarpus longan Lour.) somatic embryos and demonstrated its possible roles in cell activities during longan somatic embryogenesis (SE). However, thus far little is known of how Ran functions in the signaling pathways in plant embryos in response to changing environmental stimuli. To discover more biological roles of DlRan3A, we observed DlRan3A located in the nucleus and detected abundant accumulation of DlRan3As in globular and cotyledon embryos during longan SE, which suggested its involvement in auxin signal pathways in longan early SE. The transcript level of the DlRan3A gene were also determined in longan embryogenic callus (EC) in response to different levels of exogenous phytohormones (indoleacetic acid (IAA), gibberellin A3 (GA3), salicylic acid (SA), methyl jasmonate (MeJA), and ethephon (Eth)), salt, sucrose, prolonged culturing period and light quality treatments. IAA (1mg/L), GA3 (12mg/L), SA (75μm), MeJA (50 and 100μm), and Eth (50mg/L) modulate expression of DlRan3A to 1.3–1.4 folds, and the expression of DlRan3A was significantly affected by light quality, significantly induced to 2-fold by salt (10g/L), 2.7-fold by sucrose (90g/L) and was completely suppressed by prolonged cultivation (>40days). Deletion analysis suggested that both activation and repression regulatory elements co-exist in the DlRan3A promoter sequence and that the key cis-acting elements included ones in response to auxin, SA, MeJA, and stress. Promoter activities were induced to the highest level by IAA followed by SA, GA3 and MeJA, while suppressed by ABA and Eth. Together, these results showed DlRan3A close involvement in phytohormones, light, and abiotic stress responsiveness during longan SE.