The α-tubulin of Laodelphax striatellus facilitates the passage of rice stripe virus (RSV) and enhances horizontal transmission

Abstract

14Rice stripe virus (RSV), causal agent of rice stripe disease, is transmitted by the small 15 brown planthopper (SBPH, Laodelphax striatellus) in a persistent manner. The midgut and 16 salivary glands of SBPH are the first and last barriers in viral circulation and transmission, 17 respectively; however, the precise mechanisms used by RSV to cross these organs and 18 re-inoculate rice have not been fully elucidated. We obtained full-length cDNA of L. 19 striatellus α-tubulin 2 (LsTUB) and found that RSV infection increased the level of LsTUB 20 in vivo. Furthermore, LsTUB was shown to bind the RSV nonstructural protein 3 (NS3) in 21 vitro. RNAi was used to reduce LsTUB expression, which caused a significant reduction in 22 RSV titer, NS3 expression, RSV inoculation rates, and transmission to healthy plants. 23 Electrical penetration graphs (EPG) showed that LsTUB knockdown by RNAi did not 24 impact SBPH feeding; therefore, the reduction in RSV inoculation rate was likely caused 25 by the decrease in RSV transmission. These findings suggest that LsTUB mediates the 26 passage of RSV through midgut and salivary glands and leads to successful horizontal 27 transmission. 30The survival of plant viruses is largely dependent on the efficient transmission to plant 31 hosts by viral-specific vector(s) [1,2]. Insects transmit over 70% of all known plant viruses 32 [3]. Hemipteran insects (e.g. leafhoppers, planthoppers, aphids and whiteflies), transmit 33 approximately 55% of insect-vectored plant viruses; as these insects have distinctive 34 piercing-sucking mouthparts with needle-like stylet bundles that are comprised of two 35 maxillary and two mandibular stylets [3-5]. Four categories of insect vector -plant virus 36 transmission relationships have been described as follows: non-persistent; semi-persistent; 37 persistent: propagative and persistent: circulative [2,6]. Plant viruses with persistent 38 relationships enter vectors via the gut, pass through various tissues and ultimately reach the 39 salivary glands and ovaries. Viruses are transmitted horizontally from the salivary glands 40 of the vector into healthy plants and are vertically transmitted from female ovaries to 41 offspring [7]. Barriers to the persistent transmission of plant viruses in insect vectors 42 include the following: (i) midgut infection barriers; (ii) dissemination barriers, including 43 midgut escape and salivary gland infection barriers; (iii) salivary gland escape barriers; and 44 (iv) transovarial transmission barriers [8,9]. A deeper understanding of the mechanistic 45 basis of virus transmission through these four barriers will facilitate the development of 46 novel methods to control the systemic spread of plant viruses [10]. 47 Previous studies demonstrated that the persistent transmission of viruses in 48 different insect tissues requires specialized interactions between components of the virus 49 and vector. For example, in the aphid Myzus persicae, the coat protein read-through 50 domain (CP-RTD) of Beet western yellows virus...