Thesis’ title: “Abitotic stress resistance evaluation of rice co-overexpression of OsbZIP46CA1 and SAPK6”
Major: Genetics and plant breed selection
Supervisers: Prof. Dr. Tongmin Mou, Prof. Dr. Lizhong Xiong
Dissertation marking committee included five members:
1. Prof. Dr. Jinxiong Shen (Chairman)
2. Prof. Dr. Deming Jin (Member)
3. Prof. Dr. Shuangxia Jin (Member)
4. Prof. Dr. Jianliang Huang (Member)
5. Prof. Dr. Fazhan Qiu (Member)
The committee fully agreed to approve the PhD. Dissertation.
Here are some results gained by PhD. student:
In this study, drought-responsive genes were isolated from rice and then were assembled through multiple-round in vivo site-specific assembly (MISSA) system, and the constructs were introduced into the rice cultivar KY131 via Agrobacterium-mediated
transformation. Overexpression transgenic lines of the multi-gene and
corresponding single-gene constructs containing a single copy were
identified by analyzing the transcription level and copy number of the
transgene in T1 generation. The overexpression transgenic lines and negative transgenic plants (KY131-N) were used for pre-evaluation of drought resistant ability in the field and for further experiments.
During the pre-evaluation, co-overexpression transgenic lines of the two genes OsbZIP46CA1 (encoding a constitutively active form of the bZIP transcription factor OsbZIP46) and SAPK6 (encoding
a sucrose nonfermenting 1 [SNF1]-related protein kinase SnRK)
remarkably enhanced drought resistance compared with the single-gene
transgenic lines (CA1-OE and SAPK6-OE) and KY131-N based on visual evaluation of the leaf death and seed-setting at the reproductive stage.
The co-overexpression transgenic lines (XL22), compared with the single-gene overexpression lines and KY131-N, were hypersensitive to ABA. This suggested that the co-overexpression of OsbZIP46CA1and SAPK6 may have an additive effect on the ABA sensitivity of rice.
XL22, CA1-OE, SAPK6-OE overexpression transgenic lines and KY131-N in
drought resistance in the field using agronomical traits were further
evaluated. The results indicated that XL22 exhibited higher yield,
biomass, spikelet numbers and grain numbers under moderate drought
compared with the single-gene overexpression lines and KY131-N. The
results on water loss rate and drought stress survival rate of the
transgenic seedlings alsosupported the enhanced drought resistant
ability of XL22. Furthermore, expression profile using a RNA-Seq
analysis revealed that many genes involving in stress responses were
specifically up-regulated in the drought-treated XL22 lines and some of
the stress-related genes activated in CA1-OE and SAPK6-OEwere distinct,
which could partially explain the different performances of these lines
in response to drought resistance.
In addition, tolerance to heat (42oC) and cold (4oC)
stresses of the overexpression transgenic lines and KY131-N were tested
at the seedling stage. Results revealed that, compared with the CA1-OE, SAPK6-OE, and KY131-N, XL22 lines showed a significantly higher survival rates in both heat and cold treatments.
Besides, the malondialdehyde (MDA) content and the relative electrolyte
leakage rate of XL22 lines were also significantly lower under the heat
stress, indicating that XL22 lines have a low degree of membrane lipid
peroxidation under heat stress and partically explained the enhanced
heat resistance of XL22. These results demonstrated that overexpression
of the two genes could enhance heat and cold resistant ability of rice.
together, the results from this study suggest that the multi-gene
assembly in an appropriate combination may become a promising approach
that can be possibly applied in genetic improvement of the stress
resistance in rice.