COR, nice one, Mr Microbe!

Image: Alan Collmer, Cornell University/Wikimedia Commons.

Image: Alan Collmer, Cornell University/Wikimedia Commons.

Although open sto­mata are neces­sary for plants to take up CO2 for pho­to­syn­thesis, this also per­mits loss of pre­cious water – by tran­spir­a­tion, the so-called neces­sary evil of pho­to­syn­thesis. But, surely, noth­ing worse can be asso­ci­ated with sto­mata, can it? Well, closed sto­mata also act as a bar­rier to entry of harm­ful microbes, and they may close in response to a poten­tial threat, which is a good thing. However, some would-be invaders have man­aged to cir­cum­vent this and keep sto­mata open, thereby facil­it­at­ing their unwanted entry into the plant. Which is a neat enough trick in itself. But how they man­age this feat has been fur­ther elu­cid­ated by Xiao-yu Zheng and col­leagues and reveals the subtle molecu­lar decep­tion involved in infec­tion by the bac­terium Pseudomonas syr­ingae (which infects more than 50 plant spe­cies and is a major cause of sur­face frost dam­age in plants). The microbe pro­duces coron­at­ine (COR), which the plant can­not dis­tin­guish from jas­monic acid iso­leu­cine (JA) – which is part of the plant’s microbe defence sys­tem. So far, this sounds like a case of the bac­terium ‘shoot­ing itself in the foot’ by pro­du­cing a com­pound that should work against its own patho­genic ambi­tions. Well, that’s where the really cun­ning part comes into play. JA is only one part of the plant defences, sali­cyc­lic acid (SA) is another and plays an import­ant role but in a dif­fer­ent defence path­way. Both JA and SA inter­act, depend­ing on the type of micro­bial attack that is detec­ted, but effect­ively in oppos­i­tion to each other. JA is pro­duced in response to attack by nec­ro­trophs (that kill the plant cells); SA is made when bio­trophs (which keep plant cells alive and har­vest what they pro­duce) attack. As a JA-mimic, COR res­ults in the activ­a­tion of sev­eral tran­scrip­tion factors (‘reg­u­lat­ory molecules’ that con­trol gene expres­sion) within the plant cells that sup­press SA form­a­tion – which would oth­er­wise pro­mote sto­matal clos­ure – by affect­ing both SA bio­syn­thesis and SA meta­bol­ism. Consequently, this ‘coronatine-induced sto­matal reopen­ing’ per­mits more of the ‘biotrophs-in-necrotrophs’ cloth­ing’ to enter and invade the plant’s tis­sues. I know it’s wrong, but I just can’t help but admire this subtle pseudo­monic sub­ter­fuge. (But how does the first one get in to man­age this mag­ni­fi­cent micro­bial molecu­lar magic?). Seemingly, this type of beha­viour is not restric­ted to proka­ryotes; Ustilago may­dis, the euk­a­ryote fungus that causes eco­nom­ic­ally dam­aging corn smut of maize, is also able to sup­press the host’s patho­gen inva­sion defences. As demon­strated by Armin Djamei et al., upon infec­tion the bio­trophic fungus releases a pleth­ora of pro­teins, one of which – the enzyme choris­mate mutase (Cmu1) – effects ‘meta­bolic prim­ing’ of the infec­ted cell (and adja­cent cells), res­ult­ing even­tu­ally in reduced pro­duc­tion of… SA.

Nigel Chaffey. ORCID 0000-0002-4231-9082

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.

2 Responses

  1. Attaa says:

    i have the dried Arial parts of ground­nut plant, and i want to do anti­mi­cro­bial activ­ity on it in this lab„ may i get chance?

  2. We are report­ing work from research labs in this Cutting/blog-post. You would need to con­tact a lab involved in anti­mi­cro­bial research to see if they have suit­able screens that could help you pro­ject. Good luck!

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