Discovery Could Lead to more Pest-Resistant Crops.

A lab group in the Biological and Environmental Science and Engineering Division of KAUST has identified a protein needed by plants to mount proper defences against environmental pathogens. The role of protein MAP4K4 helps explain the tight control of immune signalling in plants and reveals targets in a molecular pathway that could be manipulated by crop breeders. “Our findings are directly applicable to make plants more resistant to pathogens,” said study author, Heribert Hirt, Professor of Plant Science at KAUST’s Desert Agriculture Initiative.

An established player in human immunity and inflammation, the role of MAP4k4 in plant disease resistance was unknown. Working with colleagues in France, the KAUST researchers—led by Hirt and postdoctoral fellow, Yunhe Jiang, made the discovery during a large screen for proteins involved in signal transduction in the weedy thale cress Arabidopsis. By studying mutant plants that lack a working copy of MAP4K4, Hirt’s team then drilled down into the core functions of this protein, revealing that showed it was essential for proper immune responses to flg22, a peptide derived from a bacterial protein found within the filamentous flagellum of disease-causing microbes.

They demonstrated that MAP4K4 directly adds chemical tags (in the form of phosphate groups) at several sites of another protein, BIK1. This helps stabilize BIK1 and promotes the production of highly toxic molecules that play a central role in pathogen resistance, explains Jiang. The researchers also showed that MAP4K4 tags a repressor of BIK1 with phosphate decorations. This chemical adornment disables the negative regulator to further promote BIK1 activation.

So far, Hirt and his lab group in the have only described this function of MAP4K4 in Arabidopsisimmunity.*

“The next step is to test our findings also in crops by generating knock-out mutants,” Hirt said. “This is quite feasible now by using CRISPR-Cas9 gene-editing technology that is established in tomato, rice and other species of agricultural importance.”