AUTHOR=Iqbal Sadia , Fosu-Nyarko John , Jones Michael G. K. 

TITLE=Attempt to Silence Genes of the RNAi Pathways of the Root-Knot Nematode, Meloidogyne incognita Results in Diverse Responses Including Increase and No Change in Expression of Some Genes

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00328

DOI=10.3389/fpls.2020.00328

ISSN=1664-462X

ABSTRACT=<p>Control of plant-parasitic nematodes (PPNs) via host-induced gene silencing (HIGS) involves rational selection of genes and detailed assessment of effects of a possible knockdown on the nematode. Some genes by nature may be very important for the survival of the nematode that knockdown may be resisted. Possible silencing and effects of 20 such genes involved in the RNA interference (RNAi) pathways of <italic>Meloidogyne incognita</italic> were investigated in this study using long double-stranded RNAs (dsRNAs) as triggers. Two of the genes, <italic>ego-1</italic> and <italic>mes-2</italic>, could not be knocked down. Expression of six genes (<italic>xpo-1</italic>, <italic>pash-1</italic>, <italic>xpo-2</italic>, <italic>rha-1</italic>, <italic>ekl-4</italic>, and <italic>csr-1</italic>) were significantly upregulated after RNAi treatment whereas for 12 of the genes, significant knockdown was achieved and with the exception of <italic>mes-2</italic> and <italic>mes-6</italic>, RNAi was accompanied by defective phenotypes in treated nematodes including various degrees of paralysis and abnormal behaviors and movement such as curling, extreme wavy movements, and twitching. These abnormalities resulted in up to 75% reduction in infectivity of a tomato host, the most affected being the J2s previously treated with dsRNA of the <italic>gfl-1</italic> gene. For 10 of the genes, effects of silencing in the J2s persisted as the adult females isolated from galls were under-developed, elongated, and transparent compared to the normal saccate, white adult females. Following RNAi of <italic>ego-1</italic>, <italic>smg-2</italic>, <italic>smg-6</italic>, and <italic>eri-1</italic>, reduced expression and/or the immediate visible effects on the J2s were not permanent as the nematodes infected and developed normally in tomato hosts. Equally intriguing was the results of RNAi of the <italic>mes-2</italic> gene where the insignificant change in gene expression and behavior of treated J2s did not mean the nematodes were not affected as they were less effective in infecting host plants. Attempt to silence <italic>drsh-1</italic>, <italic>mut-7</italic>, <italic>drh-3</italic>, <italic>rha-1</italic>, <italic>pash-1</italic>, and <italic>vig-1</italic> through HIGS led to reduction in nematode infestation by up to 89%. Our results show that genes may respond to RNAi knockdown differently so an exhaustive assessment of target genes as targets for nematode control via RNAi is imperative.</p>