Systematic analysis of HD-ZIP transcription factors in sesame genome and gene expression profiling of SiHD-ZIP class I entailing drought stress responses at early seedling stage.

Abstract

Sesame is an ancient oilseed crop, known for its high oil content and quality. Its sensitivity to drought at early seedling stage is one of the limiting factors affecting its world-wide growth and productivity. Among plant specific transcription factors, the association of HD-ZIPs with sesame drought responses at early seedling stage is not well-established yet and is very important to develop our molecular understanding on sesame drought tolerance. In this study, total 61 sesame HD-ZIP proteins were identified, based on their protein sequence homology with Arabidopsis and protein domain(s) architecture prediction, followed by their phylogenetic, conserved domain(s) motifs and gene structure analyses to classify them into four classes (HD-ZIP Class I-IV). HD-ZIP Class I was also subdivided into four subgroups: α (SiHZ25, SiHZ43, SiHZ9 and SiHZ16), β1 (SiHZ10, SiHZ30, SiHZ32 and SiHZ26), β2 (SiHZ42 and SiHZ45) and γ (SiHZ17, SiHZ7 and SiHZ35) by a comparative phylogenetic analysis of sesame with Arabidopsis and maize. Afterwards, twenty-one days old sesame seedlings were exposed to drought stress by withholding water for 7 days (when soil moisture content reduced to ~16%) and gene expression of HD-ZIP Class I (13 members) was performed in well- watered (control) and drought stressed seedlings. The gene expression analysis showed that the expressions of SiHZ7 (6.8 fold) and SiHZ35 (2.6 fold) from γ subgroup were significantly high in drought seedlings. This study is useful in demonstrating the role of SiHD-ZIP Class I in sesame drought responses at early seedling stage and to develop its novel drought tolerant varieties.