Analysis of ADP-glucose pyrophosphorylase expression during turion formation induced by abscisic acid in Spirodela polyrhiza (greater duckweed)

Abstract

BackgroundAquatic plants differ in their development from terrestrial plants in their morphology and physiology, but little is known about the molecular basis of the major phases of their life cycle. Interestingly, in place of seeds of terrestrial plants their dormant phase is represented by turions, which circumvents sexual reproduction. However, like seeds turions provide energy storage for starting the next growing season.ResultsTo begin a characterization of the transition from the growth to the dormant phase we used abscisic acid (ABA), a plant hormone, to induce controlled turion formation in Spirodela polyrhiza and investigated their differentiation from fronds, representing their growth phase, into turions with respect to morphological, ultra-structural characteristics, and starch content. Turions were rich in anthocyanin pigmentation and had a density that submerged them to the bottom of liquid medium. Transmission electron microscopy (TEM) of turions showed in comparison to fronds shrunken vacuoles, smaller intercellular space, and abundant starch granules surrounded by thylakoid membranes. Turions accumulated more than 60% starch in dry mass after two weeks of ABA treatment. To further understand the mechanism of the developmental switch from fronds to turions, we cloned and sequenced the genes of three large-subunit ADP-glucose pyrophosphorylases (APLs). All three putative protein and exon sequences were conserved, but the corresponding genomic sequences were extremely variable mainly due to the invasion of miniature inverted-repeat transposable elements (MITEs) into introns. A molecular three-dimensional model of the SpAPLs was consistent with their regulatory mechanism in the interaction with the substrate (ATP) and allosteric activator (3-PGA) to permit conformational changes of its structure. Gene expression analysis revealed that each gene was associated with distinct temporal expression during turion formation. APL2 and APL3 were highly expressed in earlier stages of turion development, while APL1 expression was reduced throughout turion development.ConclusionsThese results suggest that the differential expression of APLs could be used to enhance energy flow from photosynthesis to storage of carbon in aquatic plants, making duckweeds a useful alternative biofuel feedstock.

The Spirodela polyrhiza genome reveals insights into its neotenous reduction fast growth and aquatic lifestyle

“…The cultures were kept in a growth-chamber, maintained at 100 μmol m −2  s −1 and 23 °C through a 16 h-light, 8 h-dark photoperiod31. High molecular weight of nuclear DNA was extracted by adaption of a nuclei isolation procedure and the CTAB method35.…”

Effect of nitrogen and phosphorus deficiency on transcriptional regulation of genes encoding key enzymes of starch metabolism in duckweed ( Landoltia punctata )

“…As stated above, AGPase plays an important role in regulating starch levels and determining patterns of starch deposition in plants (Wang and Messing, 2012). Depending on the plant species, the large subunit of AGPase is known to range from 51 to 60 kDa, whereas the small subunits range from 50 to 56 kDa.…”

The clonal dependence of turion formation in the duckweed Spirodela polyrhiza—an ecogeographical approach

“…Depending upon environmental conditions, these primordia form either normal vegetative fronds, or turions. Turion cells accumulate numerous starch grains (increased starch synthesis seems to be part of the turion formation; Wang and Messing ) and develop no aerenchyma (Appenroth et al ). As a consequence, turions sink in the water body after separation from the mother fronds (Henssen ).…”