Characterization of transgenic cotton over expressing thaliana related to AGAinsensitive3/Vivparous1 and AtABI5 transcription factors: improved water use efficiency through altered guard cell physiology

Authors: FIENE, JUSTIN - Texas A&M University; MALLICK, SAYANI - Texas Tech University; MITTAL, AMANDEEP - Texas Tech University; NANSEN, CHRISTIAN - University Of California, Davis; KALNS, LAUREN - Texas A&M University; DEVER, JANE - Texas A&M University; SWORD, GREGORY - Texas A&M University; ROCK, CHRISTOPHER - Texas Tech University

Submitted to: Plant Biotechnology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2018
Publication Date: 10/14/2018
Citation: Fiene, J.G., Mallick, S., Mittal, A., Nansen, C., Kalns, L., Dever, J., Sword, G.A., Rock, C.D. 2018. Characterization of transgenic cotton (G. hirsutum L.) over expressing Arabidopsis thaliana related to AGAinsensitive3 (ABI3)/Vivparous1 (AtRAV1) and AtABI5 transcription factors: improved water use efficiency through altered guard cell physiology. Plant Biotechnology Reports. 11(5):339-353. https://doi.org/10.1007/s11816-017-0455-6.
DOI: https://doi.org/10.1007/s11816-017-0455-6

Interpretive Summary: As available water from the Ogallala Aquifer for irirgation decreases, farmers will need to reduce withdrawals from the aquifer. The use of varieties that use less irrigation water per unit of yield is one means that farmers can reduce withdrawals and maintain farm sales. However, basic knowledge of the physiological processes that contribute to efficient water use must be identified. In previous studies, cotton that was insensitive to the plant hormone abscisic acid (ABA) tended to be drought tolerant. However, the exact mechanism for this drought tolerance has not been identified. Therefore, scientists from Texas Tech University, Texas A&M University and University of California-Davis in the ARS led Ogallala Aquifer Program investigated transgenic cotton lines with genes that impart insensitivity to ABA. Results substantiate the potential for engineering drought tolerance in agricultural crops such as cotton by over-expression of these genes. This information is of value to other crop breeders and plant physiolgists working towards enhanced drought tolerance in major crops for the Southern High Plains.

Technical Abstract: In previous studies transgenic cotton (Gossypium hirsutum L.) that over-express the Arabidopsis transcription factors related to ABA-Insensitive3/Vivivparous1 (AtRAV1/2) and ABA-Insensitive5 (AtABI5) showed improved photosynthesis in the field, and greater root and leaf biomass under deficit irrigation. These findings suggested over-expression of AtRAV1/2 and AtABI5 can impact assimilate partitioning. In the present study, we investigated a subset of the same transgenic lines to further characterize expression at the protein level and address mechanisms of drought tolerance and adaptation. Specifically, we hypothesized that the transgenic lines may have enhanced responses to abscisic acid (ABA), resulting in greater water use efficiency under drought stress. We measured leaf surface temperatures (LST), stomatal density, absolute and relative sizes (i.e. pore area/guard cell area) of guard cell apertures, and ABA concentrations by mass spectrometry in cotyledons. We also characterized transgene expression in seeds by immunoblot, and stomatal conductance and photosynthesis rates in greenhouse-grown plants. Both AtRAV1 and AtABI5 over-expression lines had trends of lower levels of ABA in drought-stressed cotyledons, higher stomatal conductance and photosynthetic rates under drought in greenhouse, and lower LSTs than control Coker 312 under drought stress conditions. Notably, AtRAV1 cotyledons had significantly higher stomatal densities, and 26% smaller guard cell apertures than control line Coker 312 under drought stress, raising the possibility that smaller guard cell pores and greater stomatal densities may contribute to water use efficiencies previously measured in AtRAV1 plants in the greenhouse and field. These results are consistent with the hypothesis that over-expression of AtRAV1 resulted in an ABA hypersensitive phenotype manifest as lower levels of endogenous ABA in cotyledons associated with greater reductions in pore apertures during stress and increased stomatal density. Our results further substantiate the potential for engineering drought tolerance in agricultural crops such as cotton by over-expression of AtABI5 and AtRAVs.