Why Arabidopsis Why: High Yielding Maize Variety

-
This post is written by me as part of Why Arabidopsis Why and edited by Dr. Ian H. Street. First published in The Quiet Branches. Please follow the link below or read here.

Shoot Apical Meristem Development: Model Plant for High Yielding Crops 

Like us, plants have stem cells too. These are innate, undifferentiated cells localized in both root and shoot meristems. They house precursor cells that divide, elongate/expand, and finally form differentiated tissues and organs of plants. It’s how plants generate the roots, trunks, branches, leaves, flowers, and all the other structures we witness as the green world.

The shoot apical meristem (SAM) is a complex structure consisting of three distinct layers (denoted L1, L2 and L3) in the dicot (one of the two major groups of flowering plants) Arabidopsis thaliana. L1, L2 and L3 form the epidermis, sub-epidermal tissues, and inner tissues of the shoot, respectively [1]. Cells in the L1 and L2 layer divide in a sideways fashion, keeping these layers distinct, whereas the L3 layer divides in a more random fashion. 

Apart from the cell layers, the SAM is divided into three dynamic functional zones/cell populations. The central zone (CZ) is maintained through a low rate of cell division and supplies cells for the peripheral zone (PZ) and the rib system (see the figure below). The (PZ) is responsible for the formation of lateral organ primordial like leaves (P), whereas the rib meristem (RM) pushes the SAM upward. A group of cells residing directly below the stem cells in the CZ is referred to as the organizing center (OC) [2].




Shoot meristems are maintained by pluripotent (unspecialized with potential to become any cell type) stem cells controlled by CLAVATA-WUSCHEL feedback signaling. This pathway, which coordinates stem cell proliferation with differentiation, was first identified in Arabidopsis, but appears to be conserved in diverse higher plant species including crops. The CLAVATA3 (CLV3) - WUSCHEL (WUS) signaling pathway has evolved as the central regulatory pathway that coordinates stem cell proliferation and differentiation. This coordination is achieved via an auto-regulatory negative-feedback loop comprising the stem cell-promoting transcription factor WUS and the differentiation-promoting peptide CLV3. CLV3 – WUS maintain a circuit, where CLV3 is only expressed in stem cells of SAM and perceived by receptor like proteins in OC and repress WUS expression. Due to the repression of WUS, few stem cells are maintained and reduction in CLV3 production [3].  



To understand the function of a gene, scientists usually mutate that particular gene leading to loss-of-function (LOF – i.e. “breaking a gene”) or gain-of-function (GOF – i.e. “making more of a gene or making it more effective than usual”) phenotype of plants. Based on our knowledge about CLV3 – WUS circuit combined with mutant studies, take a look at SAM development of a crop plant, maize (Zea mays).

Through mutagenesis screening, fasciated ear 3 (fea3) mutant has been identified which contains a larger SAM like clv mutant. FEA3 is a CLV-type LRR (Leucine Rich Repeat) receptor-like gene localized to the plasma membrane. So, it was predicted that exogenous application of CLV3 would reduce SAM size. They applied CLV3 peptide to two mutants (fea2, fea3) and found that fea2 is resistant for meristem growth, but not fea3. It tells us that FEA2 perceives CLV3, not FEA3 [4].

The next idea was that FEA3 perceives something other than CLV3. According to phylogenetic analysis, three similar genes (ZmCLE7, ZmCLE14 and ZmFCP1) to CLV3 were identified in Zea mays. When these three peptides are applied exogenously on wild type plants, they reduced root growth. But, when these three peptides are applied exogenously on fea3, ZmFCP1showed resistant for root growth and SAM size also. Additionally, Zmfcp1 mutants also show fasciated ear phenotype and suggests that FEA3 – FCP1 pathway is regulating SAM signaling from differentiating cells [4].

Although CLV – WUS system is conserved from model plant Arabidopsis to crop plants, buffering of this circuit is more prominent in Arabidopsis than in crop plants. Even weak mutants of this circuit show significant phenotypes, because crop plants went through selection based on yield during domestication. Over the years, farmers selected the varieties containing increased kernel row number, kernel numbers per ear, and ear weights without considering the underlying mechanism. Comprehensive molecular biology and phenotypic study of fea3 mutant showed that high yielding variety is actually a reflection of a manipulated CLV – WUS circuit [4].  



This study from Je et al. [4] has shown the promising impact of basic research to translate into an applied field such as developing high yielding crops. At the same time it suggests a universal pathway to control cell differentiation during plant development.   

References
1.Demonstration of thethree germ layers in the shoot apex of Datura by means of induced polyploidy inpericlinal chimeras
2.Flowering anddeterminacy in Arabidopsis
3.CLAVATA-WUSCHELsignaling in the shoot meristem
4.Signaling from maizeorgan primordia via FASCIATED EAR3 regulates stem cell proliferation and yieldtraits 

Comments

Post a Comment

Popular posts

Plant Biology Highlights: Nature Articles 2018

-
Image
We are almost at the end of another year. Undoubtedly, we came across amazing research and review articles in this year. As plant biologists, we are more focused on plant-specific journals. Along with those plant-specific journals, plant-related stories are making their place into other journals too. Like previous years, this year also, I'm covering plant biology stories published in Cell, Science, and Nature all the year round. In this post, you'll find published papers from Nature.   MicroRNAs from the parasitic plant  Cuscuta campestris  target host messenger RNAs   Dodders ( Cuscuta  spp.) are obligate parasitic plants that obtain water and nutrients from the stems of host plants via specialized feeding structures called haustoria. Dodder haustoria facilitate bidirectional movement of viruses, proteins and mRNAs between host and parasite, but the functional effects of these movements are not known. Here, they showed that  Cuscut...
Read more

Ethylene: Accidental Hormone or Pheromone

-
Image
It is always fascinating how a small hydrocarbon or 2 carbon containing alkene has huge impact on plants. Yes, you gussed it right. It's Ethylene. First gaseous compound discovered as hormone. It has specific roles in fruit ripening, cell elongation, senescence, seed germination, leaf abscission, defense response and so on.   According to the definition of hormone, it should have two characteristics. Biosynthesized in a small amount by multi cellular organism and work on a distant place from the synthesis site. This classical definition for hormone was provided by Ernest Starling at 1905. Ethylene fulfills both requirement as a hormone. In addition, it can diffues and affect surrounding plants. We may consider it as pheromone in that case.   The initial discovery of ethylene is nothing but accidental observation like penicillin. In 1858, George Fahnestock observed that leaking illuminating gas are causing damage to the plants at greenhouse. During that time illum...
Read more

Mutant Series: OPEN ALL NIGHT LONG (OPAL)

-
Image
OPEN ALL NIGHT LONG. It sounds like a coffee shop or bar or club or karaoke, something like that. Interesting enough, it's a name of one Arabidopsis thaliana mutant.  Plants have an economic life as like as most other biological systems. It makes its own food using water, sunlight, and carbon dioxide. The process knows as photosynthesis. At the day time, it opens its gate/stomata. In the daytime, light is available and perfect time for cooking/photosynthesis for them. In the night, they just close the door/stomata to prevent water loss through transpiration. So, for plants, the following things happen generally in the case of stomata opening and closure.  Nighttime stomatal control is important from both evolutionary and ecological perspective.  But, the mechanism is not clear whether this dark response is simply a passive consequence of the absence of light stimulus, or an active process recruiting other mechanisms of stomatal closure or involving independ...
Read more

Black Panther: Plant Biologist's Review

-
Image
This weekend I went to the theater with friends to watch "Black Panther". Most of the times, I fall in sleep in the halfway of the movie. Fortunately, I didn't at this time. Apart from that, this movie implanted few questions in the viewer's mind. One issue is definitely about the "heart-shaped herb".  Mythology and Technology of Wakanda The story of the movie went way back to the history of Wakanda and the futuristic technological advancement of the tribe. There is a subtle link between their past and future. Their groundbreaking future technologies are based on Vibranium. In the past, the place was crashed by a huge meteorite containing Vibranium. It caused massive radiation, stayed in their environment till today and undoubtedly changed the ecology of Wakanda. It shaped the plant life in that region. The radiation-caused mutation gave rise to a diverse plant kingdom, which is rare in the other part of the world. The heart-shaped herb was o...
Read more

Plant Biology Highlights: Nature Articles 2019

-
Image
I am doing this plant biology CNS (Cell - Nature - Science) paper highlights since 2016. Every winter break, it is a fun job for me to do. I enjoy as much as writing a New Year card to my favorite person. It is also a reminder for myself that lots of great science are going on and I have to do better next year and keep trying to make a difference. Here, I have previewed plant biology stories published this year in Nature.  Mobile PEAR transcription factors integrate positional cues to prime cambial growth   Apical growth in plants initiates upon seed germination, whereas radial growth is primed only during early ontogenesis in procambium cells and activated later by the vascular cambium. Although it is not known how radial growth is organized and regulated in plants, this system resembles the developmental competence observed in some animal systems, in which pre-existing patterns of developmental potential are established early on. Here they show that in A...
Read more