Asexual and sexual reproduction in plants!

D Balasubramanian, in his latest (fortnightly) column in the Hindu, Speaking of Science, describes some of the recent research carried out at CCMB, Hyderabad (and is getting published in Nature next week a couple of weeks ago) on the genetic altering of the sexual life of plants that can lead to sustained production of high yielding plants.

The issue?

Just as we would (if we could) choose our mates with desired qualities and traits, we choose, while farming, to cross plants with desired qualities in their offspring.

These qualities are high yield, pest resistance, better fruits, more beautiful flowers and so on. In agriculture and major food crops, such well-chosen crosses lead to high yielding hybrids. The Green Revolution is the result of such an exercise.

But farmers face a problem. Once they have a good hybrid, they wish to keep its genes and propagate them by self-fertilizing the hybrid, so that the cultivars have superior yields than the parental inbred lines

Sadly though, this hybrid vigour decreases with each generation of hybrid self crossing. The copies of the different genes in the hybrid separate from each other during germ cell production, and get reshuffled in each succeeding generation. As a result we need to cross the parental lines anew each time — not a satisfactory situation.

And, is there a way out? Seems to be, and that is precisely where the CCMB researchers lead by Dr. Imran Siddiqi come in:

But there is way out. This comes from a peculiar property of many plants (and some animals such as insects and fish). Some plants such as dandelion, some berries and grasses side-step the meiosis process altogether and their seeds reproduce clonally, asexually.

The entire gene pool of the mother is passed on straight to the daughter seed. This curious, but exciting, property is referred to as apomixis, the first step of which is called apomeiosis (the apo-referring to the missing of a component).

While berries and grasses do this, major crop plants do not; they reproduce sexually. If only they could be made apomictic, we could retain hybrid vigour forever, since no reshuffling of genes as in sexual reproduction kind would occur.

If we understand the genetic and cell biological basis behind apomeiosis, we could perhaps send wheat, rice and corn along the apomixis path and produce high yielding hybrid seeds.

What are the genes controlling apomixis? It is this important issue that has been elegantly addressed and identified by Dr. Imran Siddiqi and co-workers, using the sexually reproducing plant Arabidopsis.

They show that alteration in the gene called DYAD leads to apomeiosis, sending the plant into the asexual mode. The DYAD gene normally regulates the organisation of chromosomes during meosis. Plants with mutation in DYAD, however, give rise to seeds that contain the full set of genes from the parent.

A single gene, whose function is known, can lead to a plant becoming apomictic, when its function is tampered with! This is truly a path-finding discovery and we should applaud the group for this breakthrough.

A nice piece; take a look!

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2 Responses to “Asexual and sexual reproduction in plants!”

  1. gaddeswarup Says:

    Guru,
    The paper already appeared on Feb. 28. The editor’s summary and the follow up paper by Peter J. van Dijk indicate that it is important research. I do not understand these things well, but coming from a farming background I am enthusiastic about any possibilities of improvement in agricultural yields. Here is editor’s summary:

    Editor’s Summary
    28 February 2008

    The opposite of sex

    ——————————————————————————–

    Certain plant species produce seeds that are genetically identical by an asexual process called apomixis — a botanical equivalent to the parthenogenesis found in some animals. The first step in apomixis is ‘apomeiosis’, the formation of genetically identical female gametes. Now a study of the model sexual plant Arabidopsis shows that alteration of a single gene can bring about apomeiosis, resembling an early stage in the evolution of apomixis. This finding is important for understanding the basic mechanisms of plant reproduction and also has important implications for plant breeding because the development of crop plants capable of apomixis would be highly desirable for producing high-yielding hybrid seeds.

  2. Guru Says:

    Dear Swarup,

    Thanks for the correction and pointers; I mistook Feb 28th for March 28th, I think — I have corrected the post now.

    Balasubramanian’s article gives a flavour for the problem as well as the methods of solution, and is a good introduction for people like us without the relevant background in genetics I think.

    Guru

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