Abstract
The basic helix-loop-helix (bHLH) proteins are a large family of transcription factors that control various developmental processes in eukaryotes, but the biological roles of most bHLH proteins are not very clear, especially in tomato. In this study, a PRE-like atypical bHLH gene was isolated and designated as SlPRE2 in tomato. SlPRE2 was highly expressed in immature-green fruits, moderately in young leaves, flowers, and mature-green fruits. To further research the function of SlPRE2, a 35 S:PRE2 binary vector was constructed and transformed into wild type tomato. The transgenic plants showed increased leaf angle and stem internode length, rolling leaves with decreased chlorophyll content. The water loss rate of detached leaves was increased in young transgenic lines but depressed in mature leaves. Besides, overexpression of SlPRE2 promoted morphogenesis in seedling development, producing light-green unripening fruits and yellowing ripen fruits with reduced chlorophyll and carotenoid accumulation in pericarps, respectively. Quantitative RT-PCR analysis showed that expression of the chlorophyll related genes, such as GOLDEN 2-LIKE and RbcS, were decreased in unripening 35 S:PRE2 fruit, and carotenoid biosynthesis-related genes PHYTOENE SYNTHASE1A and ζ-CAROTENE DESATURASE in ripening fruit were also down-regulated. These results suggest that SlPRE2 affects plant morphology and is a negative regulator of fruit pigment accumulation.
Highlights
The basic helix-loop-helix proteins are a large family of transcription factors that control metabolic, physiological and developmental processes in all eukaryotic organisms
Our results indicate that SlPRE2 affects plant morphogenesis, fruit chlorophyll and carotenoid accumulation probably through influencing the activity of basic helix-loop-helix (bHLH) proteins involved in light signaling
Amino acid sequence alignment of SlPRE2 and homologous proteins showed that SlPRE2 is highly homologous to AtPREs, OsBU1 and OsPGLs, which were identified as atypical bHLH18, 20, 23, 24, 28, 29 (Fig. 1a). These results indicated that SlPRE2 encodes an atypical bHLH transcription factor with no DNAbinding activity
Summary
The basic helix-loop-helix (bHLH) proteins are a large family of transcription factors that control metabolic, physiological and developmental processes in all eukaryotic organisms. They were considered to have different function based on the distinction of bHLH domain[1, 2]. The PRE3 is a dominant suppressor of BR mutant bri[1-301] and is involved in regulation of light signal transduction in Arabidopsis[24, 25]. Our results indicate that SlPRE2 affects plant morphogenesis, fruit chlorophyll and carotenoid accumulation probably through influencing the activity of bHLH proteins involved in light signaling
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