Download SP1: Improved plant performance by

Innovation in life sciences
Update July 2014 (see p2)
Evaluation and Licensing
Opportunities
For further information on this
technology and evaluation /
licensing opportunities please
contact:
Dr Jan Chojecki
[email protected]
Tel: +44 (0)1603 456500
Fax: +44 (0)1603 456552
SP1: Improved plant performance
by manipulation of plastid transition
Modifying expression of SP1 enhances many plant traits
including yield and quality and abiotic stress tolerance
Plastids having differentiated function are involved throughout plant development. As
well as chloroplasts, plastids form amyloplasts (starch storage), elaioplasts (fatty acid
Tech ID: 13.568
storage) and chromoplasts (fruit ripening), amongst others, each with a different
organisation of their organellar proteome. Plastid transition and interconversion is an
Patent Literature
essential feature of plant growth and adaptation to changing needs and conditions.
As over 90% of the proteins in plastids are nucleus-encoded and imported from the
International Publication No.
cytosol, the “TOC” machinery responsible for controlling the plastid import process is
WO2014/037735 A1
hence of crucial importance for plant function. Prof Paul Jarvis and colleagues at the
University of Leicester have identified SP1 which encodes a RING-type ubiquitin E3 ligase that associates with TOC
complexes and promotes the degradation of their components. Interestingly, the Leicester group has shown that modifying
SP1 expression can alter plastid transition and interconversion and confer a wide range of valuable performance traits on
transgenic plants.
Chloroplasts
The inventors have found that SP1 loss-of-function mutants performed plastid developmental changes inefficiently or not at
all. For example, in seedlings of sp1 mutants, heterotrophic etioplasts did not develop efficiently into chloroplasts and hence
are less able to compete for and utilise light However transgenic overexpression of SP1 in Arabidopsis increased seedling
survival significantly (33%) over wild type and also increased chlorophyll content compared to wild type (See Fig 1a, over).
At the other end of the life cycle, sp1 mutants did not convert their chloroplasts efficiently into gerontoplasts, and hence
displayed a delay in leaf senescence (Fig 1b). This informs a biotechnological approach to achieve a “staygreen” phenotype,
for enhanced source activity and yield, and improved late-season plant health, by downregulating SP1 expression in mature
vegetative tissue.
Seeds and Fruit
The inventors also compared overexpression and down-regulation of SP1 in transgenic tomato. They found that
overexpressing tomato SP1 accelerated ripening and pigmentation of tomato fruit, while downregulation delayed ripening and
pigment development (See Fig 2). Altering SP1 expression by transgenic means or mutation approaches, or even to screen
existing germplasm, could represent new ways to modify and improve fruit ripening in new varieties, or similarly to modify
amyloplast formation and enhance grain development in cereal species, or elaioplasts in oilseed crops.
Abiotic Stress
Overexpression of SP1 has been found to enhance seedling development in high-salt (150 mM NaCl) conditions, and in
addition significantly improved growth compared to WT in high osmotic stress (400 mM mannitol). Moreover, while sp1
mutants show increased sensitivity to oxidative stress (paraquat) compared WT, overexpression of SP1 greatly increased
the survival rate under paraquat treatment in transgenic Arabidopsis relative to WT. This effect correlated with reduced ROS
accumulation in SP1 overexpressors, as indicated by diaminobenzidine (DAB) staining assays.
Manipulating SP1 expression can evidently achieve different goals in different tissues and stages of plant development. The
SP1 gene is highly conserved amongst plant species and orthologues can easily be identified in dicots and monocots.
SP1 expression can be modified by transgenic approaches, or by mutagenesis, and moreover this new understanding of
SP1’s role will inform searching for existing variation in SP1 expression in association with desirable phenotypes.
References:
Ling et al. Chloroplast Biogenesis Is Regulated by Direct Action of the Ubiquitin-Proteasome System. Science: 338, 655 (2012).
TEC Release: September 2013
Updated July 2014
www.pbltechnology.com
Innovation in life sciences
Fig 1a: Survival of etiolated seedlings grown in darkness for 6 days
following transfer to continuous light for 2 days (left side).
Chlorophyll content of cotyledons of similarly-treated plants 16 h
after transfer to continuous light (right side).
Fig 1b: Mature Leaves: Delayed leaf senescence of
sp1 mutant and accelerated leaf senescence in
overexpression of SP1. Note: Senescence induced
by covering leaves with aluminium foil.
UPDATE July 2014: The leaf senescence observations have now been confirmed in maturing plants grown in the
glasshouse. SP1 overexpressors (OX) show accelerated leaf senescence, while downregulating SP1 (sp1-2) delays
senescence and prolongs photosynthetic function.
fv/fm
Ratio of leaves
100%
0.85
90%
0.8
80%
70%
0.75
60%
50%
0.7
40%
30%
0.65
20%
10%
0.6
0%
WT
WT
sp1-2
dead leave
sp1-2
OX
OX
live leave
Fig 2: Transgenic tomato.
SP1 downregulation
Fig 3a: Increased greening/development of
SP1 overexpressors (“OX”) after germinating
for 10 days on 150 mM NaCl.
Fig 3b: Increased tolerance to osmotic
stress due to SP1 overexpression:
3 weeks on 400 mM mannitol.
SP1 overexpression
Fig 3c: Increased tolerance of oxidative
stress after 10 days on medium
containing 1 µm paraquat.
The SP1 technology is the subject of pending patent applications and is available for licensing from PBL.
Prof Jarvis is relocating to the University of Oxford, October 2013
TEC Release: September 2013
Updated July 2014
www.pbltechnology.com