Plant Biology Highlights: Cell Articles 2017
It's almost the end of another amazing year. Undoubtedly, we came across amazing plant science stories all the year round. Like all other researchers, I regularly follow plant-specific journals (The Plant Cell, Plant Physiology, Nature Plants, The Plant Journal, Journal of Experimental Botany, Molecular Plant, Plant, Cell & Environment, Plant, Cell & Physiology, Frontiers in Plant Science, Plant Direct and so on). Apart from that Cell, Science, Nature, PNAS, Nature Communication and other renowned journals cover plant science stories. At the end of this 2017, I've covered few great stories from CELL in this post.
During the domestication process, farmers are looking for better traits mostly with much better productivity. All fruits are the result of flowers and the way flowers are arrayed, we call it inflorescence. By controlling the inflorescence architecture, we may get more flowers and eventually more crops. This basic concept had been employed by farmers while crop selection. But, the way farmers do it is based on "phenotype". They are totally blind to the underlying molecular mechanism. Zachary B. Lippman and his team work on the tomato inflorescence architecture. They have reported 2 mutations in MADS-box transcription factor. One mutation was selected based on flower morphology (large calyx size) and another was picked up due to the elimination of the flower abscission zone. COmbining these produce more branching, but unfortunately, increase sterility. Farmers found the repressor in that case to overcome this problem. This repressor reduces the overall productivity. Zachary B. Lippman and his team introduced a combination of natural and gene-edited MADS-box allele to create a range of inflorescence patterns. This combination helps to gain enough inflorescence and fruits at the same time. The knowledge for manipulating inflorescence pattern will be useful to translate in other crop plants too.
Another great piece of work from Zachary B. Lippman and his team was published this year on Cell. In this work, they focused on three quantitative traits: fruit size, inflorescence branching, and plant architecture. Usually, for crop engineering, we are more interested to alter a single gene. But, crop development depends on a complex array of gene regulatory network from plant development. What if we go upstream and think about promoter? Editing promoter creates a large array of cis-regulatory element pertaining to quantitative traits. From a sensitized genetic screening using CRISPR-Cas9, they selected the lines with a variation of locule number (seed compartments) and fruit size. This paper showed that the expression of major regulatory genes does not correlate with phenotype.
One of the groundbreaking papers of this year for understanding the root development during cold stress by Xu Jian's lab. It explained how root survived during chilling stress and once the stress is relieved, it continues the growth. They have shown that during chilling stress, there is selective cell death of columella stem cell daughters (CSCDs). The selective death of CSCDs helps to maintain the auxin maxima in the QC (quiescent center) and protect stem cell integrity as well as. CSCDs death helps root to survive during stress condition and comes back to normal growth state during the advent of optimal growth condition. Application of exogenous auxin (IAA) and auxin biosynthetic inhibitor (yucasin) demonstrated that maintaining auxin level is the critical criteria to withstand chilling stress in the root.
Evolution plays the vital role in our core understanding of plant science. And, for the understanding of evolutionary perspective, we need to look back the ancestor of first flowering land plants. Because flower changed the terrestrial life as it provides food for us. The known ancestor of the land plant is one charophycean alga. Understanding the genome of close ancestor will help us to reveal the biochemical, physiological and signaling pathways from the evolutionary perspective. This year the genome sequence of Marchantia polymorpha has been published. Definitely, this genome sequence has opened a new door to explore for us.
For further details regarding Marchantia polymorpha's genome database, please visit http://marchantia.info/.
Undoubtedly the most fascinating plant science story appeared in the journal this year. Every protein is synthesized in the same place and destined to a diverse location inside the cell. And, this destiny is written in their N-terminal. Abolishment of the N-terminal can easily send them the different sub-cellular location. The alteration of N-terminal may cause two ways: cleavage of N-terminal and variable starting site for protein translation. The rudimentary idea of using alternative promoter or translational start site is that it may produce several transcripts from the same gene. They have shown photoreceptor phytochrome-dependent genome-wide alternate promoter selection. Consequently, variable N-terminal and alternative localization of proteins have been observed based on light condition.
They proved this hypothesis through extensive study of glycerate kinase (GLYK). It is encoded by a single gene and usually localized in the plastid in Arabidopsis thaliana. This enzyme works in the photorespiratory pathway and metabolizes toxic 2-phosphoglycolate (2PG). As a result, the glyk mutant is lethal due to the blockage of the photorespiratory cycle. Interestingly, they have found that gGLYK-GFP (whole genomic fragment fused with GFP) is localized exclusively in the cytoplasm in darkness. They constructed two GLYK-GFP line for further investigation. ptGLYK-GFP (longer mRNA and mutated in the second ATG) and cytGLYK-GFP (shorter mRNA and does not contain the region from first ATG to second ATG). These ptGLYK-GFP and cytGLYK-GFP line only express in plastids and cytoplasm, respective. Immunoblot analysis showed that cytGLYK-GFP only accumulates in dark condition and ptGLYK-GFP accumulates regardless of light condition (both in light and dark).
This paper for the first time showed that alternate promoter selection produces the different version of same protein with altered sub-cellular localization to create functional diversity based on environmental conditions.
Communication in the Phytobiome
We communicate with each other through face to face conversation, phone call, text messages, email and sometimes via sign languages. Plants also communicate with billions of organisms from millions of species. This communication is mostly driven by the chemical signal. For instances, phytohormones are critical for plant growth and development. At the same time, plants perceive bacterial and pathogenic attack due to the activation of hormonal signaling. Salicylic acid plays the major role in the defense against biotrophic pathogens. Jasmonic acid and ethylene participate the defense against necrotrophic pathogens.
Till date our understanding about phytobiome is limited. This review tried to put together the current knowledge and future research perspective as well as.
If you are interested, you may check the Cell articles from 2016:
Plant Biology Highlights: Cell Articles 2016