Improved Wheat Growth and Yield by Delayed Leaf Senescence Using Developmentally Regulated Expression of a Cytokinin Biosynthesis Gene

Abstract

Delaying leaf senescence in plants, especially under water stress conditions, can help to maintain the remobilization of stored nutrients in source–sink relationships, thus leading to improved crop yields. Leaf senescence can be delayed by plant hormones such as cytokinin. Here, the Isopentenyl transferase (IPT) gene, encoding a cytokinin biosynthesis enzyme, driven by a modified AtMYB32xs promoter was transformed into wheat. Transgenic wheat plants exhibited delayed leaf senescence, retaining chlorophyll for longer under controlled environment conditions. Selected independent transgenic events and their corresponding nulls were grown under field conditions for two consecutive years under well-watered and water stress treatments using automated rainout shelters. Three independent transgenic events had improved canopy green cover, lower canopy temperatures, and higher leaf water potential than their respective non-transgenic nulls, with no abnormality in morphology and phenology. Increased grain yield was observed in transgenic events under both water treatments, with the yield increase more pronounced under water stress (26–42%). These results have shown that delayed leaf senescence using the chimeric transgene AtMYB32xs-p::IPT can be a useful strategy to achieve grain yield gains in wheat and potentially other crops for sustainable food production.

Role and Regulation of Cytokinins in Plant Response to Drought Stress

“…CKs modulate plant growth through changes in plant morphology and metabolism [104,[121][122][123][124], acting as the indirect factors to limit damage caused by drought stress, hence increasing the chance of plant survival under water shortage conditions (Table 1) [39,44,[125][126][127][128][129][130]. Abundant evidence exists to indicate that CKs play important roles in root growth and development in different plant species.…”

“…alter transcriptional factor-encoding genes involved in stress signaling, oxidative protection and protein modification; enhance drought tolerance [125,126] IPT (Agrobacterium tumefaciens) inducible expression stress-and maturation-induced promoter (SARK) Rice (Oryza sativa) enhance sink strength; improve drought tolerance and increase grain yield [56] IPT (Agrobacterium tumefaciens) inducible expression stress-and maturation-induced promoter (SARK) Peanut (Arachis hypogaea) maintain higher photosynthetic rates, stomatal conductance and transpiration; improve drought tolerance and increase yield under field conditions. [38] IPT (Agrobacterium tumefaciens) overexpression modified developmentally regulated transcription factor AtMYB32 (AT4G34990) promoter from Arabidopsis Canola (Brassica napus) increase higher chlorophyll levels; delay leaf senescence; enhance yield under rain-fed and irrigated conditions [127] IPT (Agrobacterium tumefaciens) inducible expression stress-and maturation-induced promoter (SARK) Cotton (Gossypium hirsutum) delay senescence; enhance root and shoot biomass; maintain higher chlorophyll content and photosynthetic rates under water deficit conditions [109] IPT (Agrobacterium tumefaciens) inducible expression stress-and maturation-induced promoter (SARK) Rice (Oryza sativa) increase drought tolerance through the coordinated regulation of carbon and nitrogen assimilation [39] IPT (Agrobacterium tumefaciens) overexpression modified developmentally regulated transcription factor AtMYB32 (AT4G34990) promoter from Arabidopsis Wheat (Triticum aestivum) increase grain yield under water deficit [44] On the other hand, an enhanced root system with less cellular damage in transgenic plants compared with the wild-type plants under drought conditions could also be achieved through increasing CK levels by using an inducible promoter to drive the expression of IPT target gene [109,110]. Another defense mechanism that has been employed by this approach is the delay of drought-induced senescence [109,111,112].…”

The Molecular Regulation of Carbon Sink Strength in Grapevine (Vitis vinifera L.)

“…This phenomenon indicated that stress-induced cytokinin synthesis in the P(SARK):IPT plants modified source/sink relationships and promoted sink strength through a cytokinin-dependent coordinated regulation of carbon and nitrogen metabolism that allowed plant adaptation and survival under water stress ( Reguera et al, 2013 ). Results in many crops that overexpress IPT under the control of P(SARK) have demonstrated a delay in leaf senescence and improved crop growth and yield under different stress conditions ( Décima Oneto et al, 2016 ; Joshi et al, 2019 ). Therefore, it appears that cytokinin plays a role in making up the deficiencies caused by stress in plant.…”

The Senescence (Stay-Green)—An Important Trait to Exploit Crop Residuals for Bioenergy

“…For example, over-expression of cytokinin biosynthetic pathway gene Isopentenyl transferase (IPT) under the control of senescence-associated promoter delayed leaf senescence in maize [20]. Over-expression of IPT gene in wheat (Triticum aestivum L.) plants resulted in delayed leaf senescence by retaining chlorophyll for longer period and resulted in markedly increased grain yields under water deficit conditions [21]. Similarly, expression of ADP-glucose pyrophosphorylase large subunit of maize in wheat seeds stimulated photosynthesis and carbon metabolism and resulting in increased seed number and total plant biomass [22].…”