Tài liệu Báo cáo khoa học: Plant a-amylase inhibitors and their interaction with insect a-amylases

REVIEW ARTICLE

Plant a-amylase inhibitors and their interaction with insect a-amylases

Structure, function and potential for crop protection

Octa vio L. Franco1,2,3, Daniel J. Rigden1

, Francislete R. Melo1,3 and Maria F. Grossi-de-SaÂ

1

1

Centro Nacional de Recursos GeneÂticos e Biotecnologia, Cenargen/Embrapa, BrasõÂlia-DF, Brazil; 2

Universidade CatoÂlica de BrasõÂlia,

BrasõÂlia-DF, Brazil; 3

Depto. de Biologia Celular, BrasõÂlia-DF, Brazil

Insect pests and pathogens (fungi, bacteria and viruses) are

responsible for severe crop losses. Insects feed directly on

the plant tissues, while the pathogens lead to damage or

death of the plant. Plants have evolved a certain degree of

resistance through the production of defence compounds,

which may be aproteic, e.g. antibiotics, alkaloids, terpenes,

cyanogenic glucosides or proteic, e.g. chitinases, b-1,3-glu￾canases, lectins, arcelins, vicilins, systemins and enzyme

inhibitors. The enzyme inhibitors impede digestion through

their action on insect gut digestive a-amylases and pro￾teinases, which play a key role in the digestion of plant

starch and proteins. The natural defences of crop plants

may be improved through the use of transgenic technology.

Current research in the area focuses particularly on weevils

as these are highly dependent on starch for their energy

supply. Six di€erent a-amylase inhibitor classes, lectin-like,

knottin-like, cereal-type, Kunitz-like, c-purothionin-like

and thaumatin-like could be used in pest control. These

classes of inhibitors show remarkable structural variety

leading to di€erent modes of inhibition and di€erent

speci®city pro®les against diverse a-amylases. Speci®city of

inhibition is an important issue as the introduced inhibitor

must not adversely a€ect the plant's own a-amylases, nor

the nutritional value of the crop. Of particular interest are

some bifunctional inhibitors with additional favourable

properties, such as proteinase inhibitory activity or chitin￾ase activity. The area has bene®ted from the recent deter￾mination of many structures of a-amylases, inhibitors and

complexes. These structures highlight the remarkable

variety in structural modes of a-amylase inhibition. The

continuing discovery of new classes of a-amylase inhibitor

ensures that exciting discoveries remain to be made. In this

review, we summarize existing knowledge of insect a-am￾ylases, plant a-amylase inhibitors and their interaction.

Positive results recently obtained for transgenic plants and

future prospects in the area are reviewed.

Keywords: a-amylase inhibitors; knottin-like; lectin-like;

thaumatin-like; Kunitz; cereal-type; bean weevils; bifunc￾tional inhibitors.

Insect pests and pathogens such as fungi, bacteria and

viruses are together, responsible for severe crop losses.

Worldwide, losses in agricultural production due to pest

attack are around 37%, with small-scale farmers hardest hit

[1]. Starchy leguminous seeds are an important staple food

and a source of dietary protein in many countries. These

seeds are rich in protein, carbohydrate and lipid and

therefore suffer extensive predation by bruchids (weevils)

and other pests. The larvae of the weevil burrow into the

seedpods and seeds and the insects usually continue to

multiply during seed storage. The damage causes extensive

losses, especially if the seeds are stored for long periods.

In general, plants contain a certain degree of resistance

against insect predation, which is re¯ected in the limited

number of insects capable of feeding on a given plant. This

resistance is the result of a set of defence mechanisms

acquired by plants during evolution [2]. It is only recently

that many secondary chemical compounds have been

de®nitively associated with plant defence, for example

through their synthesis in response to pest or pathogen

attack. Plant defences are, however, incomplete, as bruchids

and other insects are able to infest seeds and different plant

tissues despite the presence of plant defence compounds.

Two factors seem to have contributed to this phenomenon.

First, many plants suffer reductions in defence compounds

during domestication [3]. Thus, the selection of better￾tasting plants with better nutritional value has led, concom￾itantly, to crops that are more susceptible to predation.

Secondly, just as plants evolve defences, their predators

evolve means to evade those defence mechanisms; this is the

Correspondence to O. L. Franco, Centro Nacional de Recursos

GeneÂticos e Biotecnologia, Cenargen/Embrapa, S.A.I.N. Parque

Rural, Final W5, Asa Norte, Biotecnologia, Laboratory 05, CEP:

70770±900, BrasõÂlia-DF, Brazil, Fax: + 55 61 340 3624,

Tel.: + 55 61 448 4705, E-mail: [email protected]

Abbreviations: AAI, Amaranthus a-amylase inhibitor; a-AI1 and

a-AI2, a-amylase inhibitors 1 and 2 from the common bean; AMY1

and AMY2, a-amylases from barley seeds; BASI, barley a-amylase

subtilisin inhibitor; BLA, Bacillus licheniformis a-amylase; CAI,

cowpea a-amylase inhibitor; CHFI, corn Hageman factor inhibitor;

HSA, human salivary a-amylase; LCAI, Lachrima jobi chitinase/

a-amylase inhibitor; PAI, pigeonpea a-amylase inhibitor; PPA, por￾cine pancreatic a-amylase; RASI, rice a-amylase/subtilisin inhibitor;

RBI, ragi bifunctional inhibitor; SIa1, SIa2 and SIa3, Sorghum

a-amylase inhibitors 1±3; TASI, triticale a-amylase/subtilisin inhibi￾tor; TMA, Tenebrio molitor a-amylase; WASI, wheat a-amylase

subtilisin inhibitor; ZSA, Zabrotes subfasciatus a-amylase.

(Received 28 August 2001, accepted 6 November 2001)

Eur. J. Biochem. 269, 397±412 (2002) Ó FEBS 2002