642 / 2019-04-29 08:20:30

A phloem-restricted virus interacts with BREVIS RADIX domain-containing proteins and manipulates plant defense

C4,phloem,BRX

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Tomato yellow leaf curl virus (TYLCV) is a phloem-restricted geminivirus severely affecting tomato crops in most producing countries. C4 is the smallest protein (10 KDa) encoded by TYLCV; C4 is essential for the infection and localizes to plasma membrane and plasmodesmata (PD) in a myristoylation-dependent manner, although its exact molecular function is still unclear. Through a yeast two-hybrid screen we have found that C4 interacts with BREVIS RADIX (BRX) domain-containing proteins, including BRX and BRX-like 2 (BRXL2), and subsequently confirmed these interactions in vivo. Transcriptional and infection analyses indicate that BRX acts as a positive regulator of defence, and that C4 inhibits this activity. However, C4-expressing plants do not display gaps in the protophloem, unlike brx mutants. Strikingly, we also found that C4 interacts with BAM3, whose mutation restores normal phloem development in the brx background. Therefore, we hypothesize that C4 might target BRX to inhibit BRX-mediated defence responses, and BAM3 (suppressor of brx) to avoid phloem defects, potentially disadvantageous to the phloem-limited viral infection.