Lecture 2 – Plant Biotechnology I: Agriculture

Anthropological Effects

Humans have had vast and significant effects on the natural world around us. With plants, it’s mainly how we’ve domesticated and cultivated them into what they are in modern day.

Domestication

The process of humans artificially selecting perferrable traits to continue and over many generations, slowly domesticating (gradual changes) the organism.

With crops, plant breeding is the major way we’ve domesticated crops historically: done by cross-preeding plants with preferable traits to reinforce them wihtin the population

• This then results with visually distinct plants from their wild0type predecessors that aren’t as adapted to grow in the wild anymore

Plant domestication of certain crops have occurred independently and simultaneously (or at least within similar times) in several regions

Cultivation

The intentional planting and harvesting of plants (wild or domesticated)

Traditional Genetic Modification

Any sort of manipulation of an organism’s genome. With plants, it arose as a consequence of cultivation and domestication (involving artificial selection)

Artificial Selection

The repeated propagation over many generations with desired traits to reinforce those traits within the population

Breeding

The rational and intentional mating/crossing of organisms that focusses on best-performing individuals with desired traits

• This requires that individuals have varying genes so that they aren’t all the same. This creates a fitness difference.

Mutations

The actual mechanism that results in more genetic diversity and can drastically change how organisms look, grow, function, and so on.

• Breeders take advantage of genetic diversity and select those who have genes that result in desired traits to be propagated/grow

Teosinte & Corn

The wild-type version of the modern-day counterpart corn. Teosinte has very little grains, very tough husks, lots of branching stalks, and so on and so forth.

• As a crop, it has traits that are generally undesirable, make it harder to grow, results with less yields, harder to eat, and so on

Over time, with domestication of specific traits, it resulted with the corn that we know today

• Some traits we selected for include softer husks, ears that had more kernels/seed, less branching (to focus energy into one stalk), and intact seeds (non-shattering). These traits are also general traits we selected for in other crops

• Modern plants varieties and farming practises have continued to increase corn yields

Genomic Rearrangements

The deliberate change within the number of sets of chromosomes a crop may have which have occured in many modern crops. Typically results in polyploidy plants (more sets of chromosomes than normal) which tend to be bigger

Green Revolution

The noticeable increase in crop yields due to the use of more plant biotechnology (hybrid seeds, advances in plant breeding tech, etc), fertilisers, and herbicides/pesticdes/ etc.

This was needed to address the growing population and the fear of not having enough food to support it.

Hybrid Seeds

Hybridising crops often led to enhanced growth and yield, known as hybrid vigour. These hybrid plants are produced via genetic crossing through placing opposite sex organs of different plant varieties together.

• Hybrid offspring may display features of both parents, have new features, be larger, healthier, and so on (hybrid vigour is also known as heterosis)

However, their progeny will not be the same as the hybrid parents, they tend to perform worse. So, more hybrid seeds from the different parents need to be continually made

Most hybrid seeds are often leveraged by companies to produce and sell them.

Normal Borlaug

Known as the father of the Green Revolution, most famously known for developing lodging-resistant, high-yielding semi-dwarf grain (using hybridisation)

Marker Assisted Selection

The fast population growth now calls for a second Green Revolution to greatly improve yields. This is mainly done by focusing on developing drought resistant plants that require less fertiliser (more efficiently uses it).

MAS is the selection of the genotype rather than the phenotype. This makes the process of crossing plants faster because less time and resources is needed to wait for the progeny to actually express the phenotype.

• This is done by associating a genotype with a phenotype first and then linking it to a marker we can detect

Typically used by crossing our domesticated plants with other plants with desirable genotypes.

• However, this doesn’t isolate that genotype, so the rest of the genome is also crossed and mixed if it is successfully crossed (which we known with the marker)

• More crossing between the progeny w/ the markers and the domesticated crop is needed to “dilute” the other genome and make it more resemble the domesticated crop

MAS Example

An example of MAS being applied is with Sub1 rice and Swarna (domesticated) rice in India.

The domesticated rice couldn’t survive prolonged flooding (would continue growing while submerged, then would wilt). However, Sub1 rice is submergence-tolerant by halting growth during flooding to enhance survival.

MAS was used to cross Sub1 rice and Swarna rice with repeated generations to select for progeny that resemble Swarna rice but with the marker (submergence-tolerant genotype) present.

Genome-Wide Association Studies

An advancement that has allowed for more precision in the genetic modification of crops (and other organisms). GWAS involved sequencing entire genomes in order to match genes with certain traits/functions. It also can reveal the associations of parts of the genomes to a certain function.

• GWAS have shown that multiple genes are typically involved in a single trait/process/function

• It is able to reveal the genes associated with important/beneficial functions such as tolerance, disease resistance, and so on

The precision that comes with GWAS means faster times in successfully producing progeny with desired genes (less trial and error)

Modern Genetic Modification

A breeding method where one gene from another organism (plant, fungi, bacteria, etc) is integrated into the target crop.

This results in recombinant DNA where the genome still has the original crop’s genome, but with an added single gene into the genome

This precision, once again, means faster successful crosses than other breeding methods.

• A gene of interest from the other organism is isolated using molecular biology

• It is then recombined into the receipient plant’s DNA

• Once introduced, it will function and (hopefully) be expressed like any other of the genes in the genome