CO₂-Responsive CONSTANS, CONSTANS-Like, and Time of Chlorophyll a/b Binding Protein Expression1 Protein Is a Positive Regulator of Starch Synthesis in Vegetative Organs of Rice

Abstract

A unique CO 2 -Responsive CONSTANS, CONSTANS-like, and Time of Chlorophyll a/b Binding Protein1 (CCT) Protein (CRCT) containing a CCT domain but not a zinc finger motif is described, which is up-regulated under elevated CO 2 in rice (Oryza sativa). The expression of CRCT showed diurnal oscillation peaked at the end of the light period and was also increased by sugars such as glucose and sucrose. Promoter b-glucuronidase analysis showed that CRCT was highly expressed in the phloem of various tissues such as leaf blade and leaf sheath. Overexpression or RNA interference knockdown of CRCT had no appreciable effect on plant growth and photosynthesis except that tiller angle was significantly increased by the overexpression. More importantly, starch content in leaf sheath, which serves as a temporary storage organ for photoassimilates, was markedly increased in overexpression lines and decreased in knockdown lines. The expressions of several genes related to starch synthesis, such as ADP-glucose pyrophospholylase and a-glucan phospholylase, were significantly changed in transgenic lines and positively correlated with the expression levels of CRCT. Given these observations, we suggest that CRCT is a positive regulator of starch accumulation in vegetative tissues, regulating coordinated expression of starch synthesis genes in response to the levels of photoassimilates.

Characterization of sugar metabolism in the stem of Tachisuzuka, a whole-crop silage rice cultivar with high sugar content in the stem

“…Although we found many genes that were expressed differently between TS and KH ( Figure 5), these genes are not necessarily responsible for high sugar accumulation in TS because the observed differences in expression levels might result from the differences in sugar concentration between TS and KH. For example, CRCT (CO 2 -responsive CCT protein; Os05g0595300) is a transcription factor that regulates the expression of genes related to starch metabolism such as AGPL1, BE1, and Pho1 in rice stem, and its expression is known to be up-regulated by sugars, especially sucrose (Morita et al, 2015). Consistent with the findings, the expression level of CRCT was 1.8 times higher in TS than KH (Supplemental Table 2).…”

Overexpression of CO2-responsive CCT protein, a key regulator of starch synthesis strikingly increases the glucose yield from rice straw for bioethanol production

“…Therefore, the composition of rice straws of CRCT transgenic lines was analyzed (Table 1). As expected from the results of Morita et al (2015), the starch contents of CRCT overexpression lines were greatly increased compared with that of non-transgenic rice. In (2013) reported that glucose contents in liquid hydrolyzate of rice straw was varied depending on cultivars and ranged from 5.0 to 24.5 g per 100 g DW among 13 rice cultivars in Japan.…”

“…This defect in yield should be improved and can be overcome by the modification of genetic engineering. In our transgenic line, CRCT was overexpressed using the actin promoter which provides high levels of constitutive expression (Morita et al, 2015). The constitutive enhancement of starch synthesis could reduce the partitioning of photoassimilates to the reproductive organ when needed for its development.…”

“…In our previous study, we showed that a novel CONSTANS, CONSTANS-like and TOC1 (CCT) domain-containing protein, named CO 2 -responsive CCT Protein (CRCT), is a positive regulator of starch synthesis in vegetative organ of rice (Morita et al, 2015). Interestingly, the overexpression of CRCT greatly increased the starch content of straw in rice.…”

“…Nipponbare), CRCT overexpression lines and CRCT RNAi knockdown line were used in this study (Morita et al, 2015). In CRCT overexpression lines, the full length coding region of CRCT cDNA was constitutively overexpressed using rice actin promotor.…”