Research Article: A study of CCD8 genes/proteins in seven monocots and eight dicots

Date Published: March 12, 2019

Publisher: Public Library of Science

Author(s): Ritu Batra, Priyanka Agarwal, Sandhya Tyagi, Dinesh Kumar Saini, Vikas Kumar, Anuj Kumar, Sanjay Kumar, Harindra Singh Balyan, Renu Pandey, Pushpendra Kumar Gupta, Guangyuan He.


In plants, the enzyme CCD8 (carotenoid cleavage dioxygenase 8) is involved in the synthesis of an important hormone, strigolactone, and therefore, plays an important role in controlling growth and development. Using cDNA and protein sequence derived from the gene ZmCCD8 from maize, we identified putative orthologs of the gene encoding CCD8 in six other monocots and eight dicots; the sequence similarity ranged from 52–75.9% at the gene level and 60.9–93.7% at the protein level. The average length of the gene was ~3.3 kb (range: 2.08 to 3.98 kb), although the number of introns within the genes differed (4 or 5 in dicots and 3 or 4 in monocots, except in T. urartu with 6 introns). Several cis-acting regulatory elements were identified in the promoters of CCD8 genes, which are known to respond to biotic and abiotic stresses. The N-terminal end (up to ~70 amino acids) of CCD8 proteins was highly variable due to insertions, deletions and mismatches. The variation in genes and proteins were particularly conspicuous in T. urartu and Ae. tauschii among the monocots and A. thaliana and P. persica among the dicots. In CCD8 proteins, 12 motifs were also identified, of which 6 were novel; 4 of these novel motifs occurred in all the 15 species. The 3D structures of proteins had the characteristic features of the related enzyme apocarotenoid oxygenase (ACO) of Synechocystis (a representative of cyanobacteria). The results of qRT-PCR in wheat revealed that under phosphorous (P)-starved condition (relative to expression under optimum P used as control), the expression of TaCCD8 genes increased ~37 fold in root tissue of the cultivar C306 and ~33 fold in shoot tissue of the cultivar HUW468 (the two cultivars differed in their P-use efficiency). This suggested that expression of TaCCD8 genes is genotype-dependent and tissue-specific and is regulated under different levels of P supply.

Partial Text

In plants, CCD8 (carotenoid cleavage dioxygenase 8) is an important enzyme belonging to the family of CCD enzymes. They derive their name from the fact that the CCD-mediated reactions involve cleavage of carotenoids, involving use of dioxygen or molecular oxygen (O2). The cleavage products in most cases are apocarotenoids, which carry each an aldehyde or ketone group at the cleavage site. CCDs are further classified into CCD1, CCD2, CCD4, CCD7 and CCD8 on the basis of cleavage position and/or their substrate preferences [1,2]. In different plant species, the CCD8 is also known by the following different names: MAX4 (Arabidopsis), RMS1 (pea), D10 (rice), and DAD1 (petunia) [1,2].




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